diff --git a/include/mitsuba/core/bitmap.h b/include/mitsuba/core/bitmap.h
index d7f58d73..0884fb54 100644
--- a/include/mitsuba/core/bitmap.h
+++ b/include/mitsuba/core/bitmap.h
@@ -403,7 +403,7 @@ public:
 	void colorBalance(Float r, Float g, Float b);
 
 	/// Draw a filled rectangle with the specified position and size
-	void fill(const Point2i &offset, const Vector2i &size, const Spectrum &value);
+	void fillRect(Point2i offset, Vector2i size, const Spectrum &value);
 
 	/// Bitmap equality operator (useful for unit-tests etc.)
 	bool operator==(const Bitmap &bitmap) const;
@@ -699,7 +699,25 @@ public:
 	 * use different component formats or channels, or when the
 	 * component format is \ref EBitmask.
 	 */
-	void accumulate(const Bitmap *bitmap, const Point2i &offset);
+	void accumulate(const Bitmap *bitmap, Point2i sourceOffset,
+			Point2i targetOffset, Vector2i size);
+
+	/**
+	 * \brief Accumulate the contents of another bitmap into the
+	 * region of the specified offset
+	 *
+	 * This convenience function calls the main <tt>accumulate()</tt>
+	 * implementation with <tt>size</tt> set to <tt>bitmap->getSize()</tt>
+	 * and <tt>sourceOffset</tt> set to zero. Out-of-bounds regions are
+	 * ignored. It is assumed that <tt>bitmap != this</tt>.
+	 *
+	 * \remark This function throws an exception when the bitmaps
+	 * use different component formats or channels, or when the
+	 * component format is \ref EBitmask.
+	 */
+	inline void accumulate(const Bitmap *bitmap, Point2i targetOffset) {
+		accumulate(bitmap, Point2i(0), targetOffset, bitmap->getSize());
+	}
 
 	/**
 	 * \brief Up- or down-sample this image to a different resolution
diff --git a/include/mitsuba/hw/font.h b/include/mitsuba/hw/font.h
index 55ed0ac0..c157237d 100644
--- a/include/mitsuba/hw/font.h
+++ b/include/mitsuba/hw/font.h
@@ -76,12 +76,22 @@ public:
 	/// Allocate memory for a certain font
 	Font(EFont font);
 
+	/// Draw text to the specified bitmap
+	void drawText(Bitmap *dest, Point2i pos, const std::string &text) const;
+
+	/// Compute the size covered by the given string when rendered using this font
+	Vector2i getSize(const std::string &text) const;
+
 	/// Upload the font to the GPU
 	void init(Renderer *renderer);
 
 	/// Free the GPU memory
 	void cleanup();
 
+	/// Convert the underlying bitmap to a different pixel format
+	void convert(Bitmap::EPixelFormat pixelFormat,
+		Bitmap::EComponentFormat componentFormat, Float gamma);
+
 	/// Return the name of this font
 	inline const std::string &getName() const { return m_name; }
 
diff --git a/src/films/hdrfilm.cpp b/src/films/hdrfilm.cpp
index adac3f14..967e5900 100644
--- a/src/films/hdrfilm.cpp
+++ b/src/films/hdrfilm.cpp
@@ -20,6 +20,7 @@
 #include <mitsuba/core/fstream.h>
 #include <mitsuba/core/bitmap.h>
 #include <mitsuba/core/statistics.h>
+#include <mitsuba/hw/font.h>
 #include <boost/algorithm/string.hpp>
 #include "banner.h"
 
@@ -114,7 +115,33 @@ MTS_NAMESPACE_BEGIN
  *     <boolean name="banner" value="false"/>
  * </film>
  * \end{xml}
-
+ *
+ * \subsubsection*{Annotations:}
+ * \label{sec:film-annotations}
+ * The \pluginref{ldrfilm} and \pluginref{hdrfilm} plugins support an additional
+ * feature referred to as \emph{annotations}, which can be quite useful under
+ * certain circumstances.
+ *
+ * Annotations are used to embed useful information inside a rendered image so
+ * that this information is later available to anyone viewing the image.
+ * Exemplary uses of this feature might be to store the frame or take number,
+ * camera parameters, or other relevant scene information.
+ *
+ * Annotations can either be created by means of a \emph{tag}, which is an entry
+ * in the metadata table of the image file (does not modify the actual image data),
+ * or a \emph{text} label which is ``burned'' into the image.
+ *
+ * The syntax of this looks as follows:
+ *
+ * \begin{xml}
+ * <film type="ldrfilm">
+ * 	<!-- Create a new metadata entry 'my_tag_name' and set it to the value 'my_tag_value' -->
+ * 	<string name="tag('my_tag_name')" value="my_tag_value"/>
+ *
+ * 	<!-- Add the label 'Hello' at the image position X=50, Y=80 -->
+ * 	<string name="text(50,80)" value="Hello!"/>
+ * </film>
+ * \end{xml}
  */
 class HDRFilm : public Film {
 public:
@@ -204,6 +231,25 @@ public:
 
 		}
 
+		std::vector<std::string> keys = props.getPropertyNames();
+		for (size_t i=0; i<keys.size(); ++i) {
+			std::string key = boost::to_lower_copy(keys[i]);
+
+			if (boost::starts_with(key, "tag('") && boost::ends_with(key, "')")) {
+				m_tags[keys[i].substr(5, key.length()-7)] = props.getString(keys[i]);
+			} else if (boost::starts_with(key, "text(") && boost::ends_with(key, ")")) {
+				std::vector<std::string> args = tokenize(key.substr(5, key.length()-6), " ,");
+
+				if (args.size() != 2)
+					Log(EError, "Text command '%s' has an invalid number of arguments!", key.c_str());
+
+				Annotation annotation;
+				annotation.offset = Point2i(atoi(args[0].c_str()), atoi(args[1].c_str()));
+				annotation.text = props.getString(keys[i]);
+				m_annotations.push_back(annotation);
+			}
+		}
+
 		m_storage = new ImageBlock(Bitmap::ESpectrumAlphaWeight, m_cropSize);
 	}
 
@@ -321,6 +367,23 @@ public:
 			}
 		}
 
+		if (!m_annotations.empty()) {
+			ref<Font> font = new Font(Font::EBitstreamVeraMono14);
+			font->convert(bitmap->getPixelFormat(), bitmap->getComponentFormat(), 1.0f);
+
+			for (size_t i=0; i<m_annotations.size(); ++i) {
+				const Point2i &offset = m_annotations[i].offset;
+				const std::string &text = m_annotations[i].text;
+				Vector2i size = font->getSize(text);
+				bitmap->fillRect(offset-Vector2i(4, 4), size + Vector2i(8, 8), Spectrum(0.0f));
+				font->drawText(bitmap, offset, text);
+			}
+		}
+
+		for (std::map<std::string, std::string>::const_iterator it = m_tags.begin();
+				it != m_tags.end(); ++it)
+			bitmap->getMetadata()[it->first] = it->second;
+
 		fs::path filename = m_destFile;
 		std::string extension = boost::to_lower_copy(filename.extension().string());
 		std::string properExtension = (m_fileFormat == Bitmap::EOpenEXR) ? ".exr" : ".rgbe";
@@ -367,6 +430,11 @@ public:
 
 	MTS_DECLARE_CLASS()
 protected:
+	struct Annotation {
+		Point2i offset;
+		std::string text;
+	};
+
 	Bitmap::EFileFormat m_fileFormat;
 	Bitmap::EPixelFormat m_pixelFormat;
 	Bitmap::EComponentFormat m_componentFormat;
@@ -374,6 +442,9 @@ protected:
 	bool m_attachLog;
 	fs::path m_destFile;
 	ref<ImageBlock> m_storage;
+
+	std::vector<Annotation> m_annotations;
+	std::map<std::string, std::string> m_tags;
 };
 
 MTS_IMPLEMENT_CLASS_S(HDRFilm, false, Film)
diff --git a/src/films/ldrfilm.cpp b/src/films/ldrfilm.cpp
index b26f2ca1..eab41b11 100644
--- a/src/films/ldrfilm.cpp
+++ b/src/films/ldrfilm.cpp
@@ -20,6 +20,7 @@
 #include <mitsuba/core/fstream.h>
 #include <mitsuba/core/bitmap.h>
 #include <mitsuba/core/statistics.h>
+#include <mitsuba/hw/font.h>
 #include <boost/algorithm/string.hpp>
 #include "banner.h"
 
@@ -113,6 +114,9 @@ MTS_NAMESPACE_BEGIN
  * The RGB values exported by this plugin correspond to the ITU-R Rec. BT. 709-3
  * primaries with a D65 white point. When $\texttt{gamma}$ is set to $\code{-1}$ (the default),
  * the output is in the sRGB color space and will display as intended on compatible devices.
+ *
+ * Note that this plugin supports render-time \emph{annotations}, which
+ * are described on page~\pageref{sec:film-annotations}.
  */
 class LDRFilm : public Film {
 public:
@@ -176,6 +180,25 @@ public:
 		m_reinhardKey = props.getFloat("key", 0.18f);
 		m_reinhardBurn = props.getFloat("burn", 0.0);
 
+		std::vector<std::string> keys = props.getPropertyNames();
+		for (size_t i=0; i<keys.size(); ++i) {
+			std::string key = boost::to_lower_copy(keys[i]);
+
+			if (boost::starts_with(key, "tag('") && boost::ends_with(key, "')")) {
+				m_tags[keys[i].substr(5, key.length()-7)] = props.getString(keys[i]);
+			} else if (boost::starts_with(key, "text(") && boost::ends_with(key, ")")) {
+				std::vector<std::string> args = tokenize(key.substr(5, key.length()-6), " ,");
+
+				if (args.size() != 2)
+					Log(EError, "Text command '%s' has an invalid number of arguments!", key.c_str());
+
+				Annotation annotation;
+				annotation.offset = Point2i(atoi(args[0].c_str()), atoi(args[1].c_str()));
+				annotation.text = props.getString(keys[i]);
+				m_annotations.push_back(annotation);
+			}
+		}
+
 		m_storage = new ImageBlock(Bitmap::ESpectrumAlphaWeight, m_cropSize);
 	}
 
@@ -313,6 +336,23 @@ public:
 			}
 		}
 
+		if (!m_annotations.empty()) {
+			ref<Font> font = new Font(Font::EBitstreamVeraMono14);
+			font->convert(bitmap->getPixelFormat(), bitmap->getComponentFormat(), m_gamma);
+
+			for (size_t i=0; i<m_annotations.size(); ++i) {
+				const Point2i &offset = m_annotations[i].offset;
+				const std::string &text = m_annotations[i].text;
+				Vector2i size = font->getSize(text);
+				bitmap->fillRect(offset-Vector2i(4, 4), size + Vector2i(8, 8), Spectrum(0.0f));
+				font->drawText(bitmap, offset, text);
+			}
+		}
+
+		for (std::map<std::string, std::string>::const_iterator it = m_tags.begin();
+				it != m_tags.end(); ++it)
+			bitmap->getMetadata()[it->first] = it->second;
+
 		fs::path filename = m_destFile;
 		std::string extension = boost::to_lower_copy(filename.extension().string());
 		std::string expectedExtension;
@@ -367,6 +407,11 @@ public:
 
 	MTS_DECLARE_CLASS()
 protected:
+	struct Annotation {
+		Point2i offset;
+		std::string text;
+	};
+
 	Bitmap::EFileFormat m_fileFormat;
 	Bitmap::EPixelFormat m_pixelFormat;
 	bool m_hasBanner;
@@ -375,6 +420,9 @@ protected:
 	ref<ImageBlock> m_storage;
 	ETonemapMethod m_tonemapMethod;
 	Float m_exposure, m_reinhardKey, m_reinhardBurn;
+
+	std::vector<Annotation> m_annotations;
+	std::map<std::string, std::string> m_tags;
 };
 
 MTS_IMPLEMENT_CLASS_S(LDRFilm, false, Film)
diff --git a/src/films/tiledhdrfilm.cpp b/src/films/tiledhdrfilm.cpp
index 0f15b59e..73751155 100644
--- a/src/films/tiledhdrfilm.cpp
+++ b/src/films/tiledhdrfilm.cpp
@@ -432,7 +432,7 @@ public:
 
 	bool develop(const Point2i &sourceOffset, const Vector2i &size,
 			const Point2i &targetOffset, Bitmap *target) const {
-		target->fill(targetOffset, size, Spectrum(0.0f));
+		target->fillRect(targetOffset, size, Spectrum(0.0f));
 		return false; /* Not supported by the tiled EXR film! */
 	}
 
diff --git a/src/libcore/bitmap.cpp b/src/libcore/bitmap.cpp
index a29cc62d..0419ff54 100644
--- a/src/libcore/bitmap.cpp
+++ b/src/libcore/bitmap.cpp
@@ -430,47 +430,59 @@ void Bitmap::flipVertically() {
 	}
 }
 
-void Bitmap::accumulate(const Bitmap *bitmap, const Point2i &offset) {
+
+void Bitmap::accumulate(const Bitmap *bitmap, Point2i sourceOffset,
+		Point2i targetOffset, Vector2i size) {
 	Assert(getPixelFormat() == bitmap->getPixelFormat() &&
 	       getComponentFormat() == bitmap->getComponentFormat() &&
 	       getChannelCount() == bitmap->getChannelCount());
 
-	const int
-		offsetX = std::max(offset.x, 0),
-		offsetY = std::max(offset.y, 0),
-		endX    = std::min(offset.x + bitmap->getSize().x, m_size.x),
-		endY    = std::min(offset.y + bitmap->getSize().y, m_size.y);
+	Vector2i offsetIncrease(
+		std::max(0, std::max(-sourceOffset.x, -targetOffset.x)),
+		std::max(0, std::max(-sourceOffset.y, -targetOffset.y))
+	);
 
-	if (offsetX >= endX || offsetY >= endY)
+	sourceOffset += offsetIncrease;
+	targetOffset += offsetIncrease;
+	size -= offsetIncrease;
+
+	Vector2i sizeDecrease(
+		std::max(0, std::max(sourceOffset.x + size.x - bitmap->getWidth(), targetOffset.x + size.x - getWidth())),
+		std::max(0, std::max(sourceOffset.y + size.y - bitmap->getWidth(), targetOffset.y + size.y - getWidth())));
+
+	size -= sizeDecrease;
+
+	if (size.x <= 0 || size.y <= 0)
 		return;
 
 	const size_t
-		columns      = (endX - offsetX) * m_channelCount,
+		columns      = size.x * m_channelCount,
 		pixelStride  = getBytesPerPixel(),
-		sourceStride = bitmap->getSize().x * pixelStride,
-		targetStride = m_size.x * pixelStride;
+		sourceStride = bitmap->getWidth() * pixelStride,
+		targetStride = getWidth() * pixelStride;
 
 	const uint8_t *source = bitmap->getUInt8Data() +
-		(offsetX - offset.x + (offsetY - offset.y) * bitmap->getSize().x) * pixelStride;
+		(sourceOffset.x + sourceOffset.y * (size_t) bitmap->getWidth()) * pixelStride;
 
 	uint8_t *target = m_data +
-		(offsetX + offsetY * m_size.x) * pixelStride;
+		(targetOffset.x + targetOffset.y * (size_t) m_size.x) * pixelStride;
 
-	for (int y = offsetY; y < endY; ++y) {
+	for (int y = 0; y < size.y; ++y) {
 		switch (m_componentFormat) {
 			case EUInt8:
 				for (size_t i = 0; i < columns; ++i)
-					((uint8_t *) target)[i] += ((uint8_t *) source)[i];
+					((uint8_t *) target)[i] = (uint8_t) std::min(0xFF, ((uint8_t *) source)[i] + ((uint8_t *) target)[i]);
+
 				break;
 
 			case EUInt16:
 				for (size_t i = 0; i < columns; ++i)
-					((uint16_t *) target)[i] += ((uint16_t *) source)[i];
+					((uint16_t *) target)[i] = (uint16_t) std::min(0xFFFF, ((uint16_t *) source)[i] + ((uint16_t *) target)[i]);
 				break;
 
 			case EUInt32:
 				for (size_t i = 0; i < columns; ++i)
-					((uint32_t *) target)[i] += ((uint32_t *) source)[i];
+					((uint32_t *) target)[i] = std::min((uint32_t) 0xFFFFFFFFUL, ((uint32_t *) source)[i] + ((uint32_t *) target)[i]);
 				break;
 
 			case EFloat16:
@@ -554,8 +566,9 @@ void Bitmap::setPixel(const Point2i &pos, const Spectrum &value) {
 }
 
 void Bitmap::drawHLine(int y, int x1, int x2, const Spectrum &value) {
-	AssertEx( y >= 0 &&  y < m_size.y &&
-	         x1 >= 0 && x2 < m_size.x, "Bitmap::drawVLine(): out of bounds!");
+	if (y < 0 || y >= m_size.y)
+		return;
+	x1 = std::max(x1, 0); x2 = std::min(x2, m_size.x-1);
 
 	const FormatConverter *cvt = FormatConverter::getInstance(
 		std::make_pair(EFloat, m_componentFormat)
@@ -574,8 +587,9 @@ void Bitmap::drawHLine(int y, int x1, int x2, const Spectrum &value) {
 }
 
 void Bitmap::drawVLine(int x, int y1, int y2, const Spectrum &value) {
-	AssertEx( x >= 0 &&  x < m_size.x &&
-	         y1 >= 0 && y2 < m_size.y, "Bitmap::drawVLine(): out of bounds!");
+	if (x < 0 || x >= m_size.x)
+		return;
+	y1 = std::max(y1, 0); y2 = std::min(y2, m_size.y-1);
 
 	const FormatConverter *cvt = FormatConverter::getInstance(
 		std::make_pair(EFloat, m_componentFormat)
@@ -601,9 +615,12 @@ void Bitmap::drawRect(const Point2i &offset, const Vector2i &size, const Spectru
 	drawVLine(offset.x + size.x - 1, offset.y, offset.y + size.y - 1, value);
 }
 
-void Bitmap::fill(const Point2i &offset, const Vector2i &size, const Spectrum &value) {
-	AssertEx(offset.x >= 0 && offset.x + size.x <= m_size.x &&
-	         offset.y >= 0 && offset.y + size.y <= m_size.y, "Bitmap::fill(): out of bounds!");
+void Bitmap::fillRect(Point2i offset, Vector2i size, const Spectrum &value) {
+	int sx = std::max(0, -offset.x), sy = std::max(0, -offset.y);
+	size.x -= sx; size.y -= sy; offset.x += sx; offset.y += sy;
+
+	size.x -= std::max(0, offset.x + size.x - m_size.x);
+	size.y -= std::max(0, offset.y + size.y - m_size.y);
 
 	const FormatConverter *cvt = FormatConverter::getInstance(
 		std::make_pair(EFloat, m_componentFormat)
diff --git a/src/libhw/font.cpp b/src/libhw/font.cpp
index dc705f3c..8f288c40 100644
--- a/src/libhw/font.cpp
+++ b/src/libhw/font.cpp
@@ -74,6 +74,70 @@ Font::Font(EFont font) {
 	dscStream->read(m_kerningMatrix, 256*256);
 }
 
+void Font::convert(Bitmap::EPixelFormat pixelFormat, Bitmap::EComponentFormat componentFormat, Float gamma) {
+	m_bitmap = m_bitmap->convert(pixelFormat, componentFormat, gamma);
+}
+
+void Font::drawText(Bitmap *dest, Point2i pos, const std::string &text) const {
+	int initial = pos.x;
+
+	for (size_t i=0; i<text.length(); i++) {
+		char character = text[i];
+		if (character == '\r')
+			continue;
+		if (character == '\n') {
+			pos.x = initial;
+			pos.y += (int) (getMaxVerticalBearing()*4.0/3.0);
+			continue;
+		}
+
+		const Font::Glyph &glyph = getGlyph(character);
+
+		Point2i targetOffset = pos + Vector2i(
+			glyph.horizontalBearing,
+			getMaxVerticalBearing() - glyph.verticalBearing - 1
+		);
+
+		Point2i sourceOffset(
+			glyph.tx.x * m_bitmap->getWidth(),
+			glyph.tx.y * m_bitmap->getHeight());
+
+		dest->accumulate(m_bitmap.get(), sourceOffset, targetOffset, glyph.size);
+
+		pos.x += glyph.horizontalAdvance;
+
+		if (i+1 < text.length())
+			pos.x += getKerning(character, text[i+1]);
+	}
+}
+
+Vector2i Font::getSize(const std::string &text) const {
+	Vector2i size(0, getMaxVerticalBearing());
+	int pos = 0;
+
+	for (size_t i=0; i<text.length(); i++) {
+		char character = text[i];
+		if (character == '\r')
+			continue;
+		if (character == '\n') {
+			size.y += getMaxVerticalBearing()*(4.0 / 3.0);
+			size.x = std::max(size.x, pos);
+			pos = 0;
+			continue;
+		}
+
+		const Font::Glyph &glyph = getGlyph(character);
+
+		pos += glyph.horizontalAdvance;
+
+		if (i+1 < text.length())
+			pos += getKerning(character, text[i+1]);
+	}
+	size.x = std::max(size.x, pos);
+
+	return size;
+}
+
 void Font::init(Renderer *renderer) {
 	m_texture = renderer->createGPUTexture(m_name, m_bitmap);
 	m_texture->setFilterType(GPUTexture::ENearest);
diff --git a/src/libpython/core.cpp b/src/libpython/core.cpp
index ab13f2a4..b0e0cb0b 100644
--- a/src/libpython/core.cpp
+++ b/src/libpython/core.cpp
@@ -708,6 +708,9 @@ void export_core() {
 		.def("clear", &InterpolatedSpectrum::clear)
 		.def("zeroExtend", &InterpolatedSpectrum::zeroExtend);
 
+	void (Bitmap::*accumulate_1)(const Bitmap *bitmap, Point2i sourceOffset, Point2i targetOffset, Vector2i size) = &Bitmap::accumulate;
+	void (Bitmap::*accumulate_2)(const Bitmap *bitmap, Point2i targetOffset) = &Bitmap::accumulate;
+
 	BP_CLASS(Bitmap, Object, (bp::init<Bitmap::EPixelFormat, Bitmap::EComponentFormat, const Vector2i &>()))
 		.def(bp::init<Bitmap::EPixelFormat, Bitmap::EComponentFormat, const Vector2i &, int>())
 		.def(bp::init<Bitmap::EFileFormat, Stream *>())
@@ -716,7 +719,8 @@ void export_core() {
 		.def("expand", &Bitmap::expand, BP_RETURN_VALUE)
 		.def("flipVertically", &Bitmap::flipVertically)
 		.def("crop", &Bitmap::crop)
-		.def("accumulate", &Bitmap::accumulate)
+		.def("accumulate", accumulate_1)
+		.def("accumulate", accumulate_2)
 		.def("clear", &Bitmap::clear)
 		.def("write", &Bitmap::write)
 		.def("setString", &Bitmap::setString)