diff --git a/dive.c b/dive.c
index 758368615..fc0fbb855 100644
--- a/dive.c
+++ b/dive.c
@@ -392,6 +392,7 @@ static void copy_pl(struct picture *sp, struct picture *dp)
 {
 	*dp = *sp;
 	dp->filename = copy_string(sp->filename);
+	dp->hash = copy_string(sp->hash);
 }
 
 /* copy an element in a list of tags */
@@ -2936,6 +2937,7 @@ static void picture_free(struct picture *p)
 	if (!p)
 		return;
 	free(p->filename);
+	free(p->hash);
 	free(p);
 }
 void dive_remove_picture(char *filename)
diff --git a/dive.h b/dive.h
index 91c160e1f..e189b860d 100644
--- a/dive.h
+++ b/dive.h
@@ -366,6 +366,7 @@ struct dive_components {
 /* picture list and methods related to dive picture handling */
 struct picture {
 	char *filename;
+	char *hash;
 	offset_t offset;
 	degrees_t latitude;
 	degrees_t longitude;
diff --git a/load-git.c b/load-git.c
index 053a7140e..be25e8e94 100644
--- a/load-git.c
+++ b/load-git.c
@@ -828,6 +828,12 @@ static void parse_picture_gps(char *line, struct membuffer *str, void *_pic)
 	pic->longitude = parse_degrees(line, &line);
 }
 
+static void parse_picture_hash(char *line, struct membuffer *str, void *_pic)
+{
+	struct picture *pic = _pic;
+	pic->hash = get_utf8(str);
+}
+
 /* These need to be sorted! */
 struct keyword_action dc_action[] = {
 #undef D
@@ -900,7 +906,7 @@ static void settings_parser(char *line, struct membuffer *str, void *_unused)
 static struct keyword_action picture_action[] = {
 #undef D
 #define D(x) { #x, parse_picture_ ## x }
-	D(filename), D(gps)
+	D(filename), D(gps), D(hash)
 };
 
 static void picture_parser(char *line, struct membuffer *str, void *_pic)
diff --git a/parse-xml.c b/parse-xml.c
index 90559d6c4..a42f8c854 100644
--- a/parse-xml.c
+++ b/parse-xml.c
@@ -1296,6 +1296,8 @@ static void try_to_fill_dive(struct dive *dive, const char *name, char *buf)
 		return;
 	if (MATCH("gps.picture", gps_picture_location, cur_picture))
 		return;
+	if (MATCH("hash.picture", utf8_string, &cur_picture->hash))
+		return;
 	if (MATCH("cylinderstartpressure", pressure, &dive->cylinder[0].start))
 		return;
 	if (MATCH("cylinderendpressure", pressure, &dive->cylinder[0].end))
diff --git a/qt-ui/divepicturewidget.cpp b/qt-ui/divepicturewidget.cpp
index 92695b6a6..a0d209b6d 100644
--- a/qt-ui/divepicturewidget.cpp
+++ b/qt-ui/divepicturewidget.cpp
@@ -3,7 +3,25 @@
 #include "dive.h"
 #include "divelist.h"
 #include <QtConcurrentMap>
+#include <QtConcurrentRun>
 #include <QDir>
+#include <QCryptographicHash>
+#include <mainwindow.h>
+#include <qthelper.h>
+
+SHashedImage::SHashedImage(struct picture *picture) : QImage(picture->filename)
+{
+	if (isNull()) {
+		// Hash lookup.
+		load(fileFromHash(picture->hash));
+		if (!isNull())
+			QtConcurrent::run(updateHash, picture);
+	} else {
+		QByteArray hash = hashFile(QString(picture->filename));
+		free(picture->hash);
+		picture->hash = strdup(hash.toHex().data());
+	}
+}
 
 DivePictureModel *DivePictureModel::instance()
 {
@@ -15,20 +33,21 @@ DivePictureModel::DivePictureModel() : numberOfPictures(0)
 {
 }
 
-typedef QPair<QString, QImage> SPixmap;
-typedef QList<SPixmap> SPixmapList;
+typedef struct picture *picturepointer;
+typedef QPair<picturepointer, QImage> SPixmap;
+typedef QList<struct picture *> SPictureList;
 
-SPixmap scaleImages(const QString &s)
+SPixmap scaleImages(picturepointer picture)
 {
 	static QHash <QString, QImage > cache;
 	SPixmap ret;
-	ret.first = s;
-	if (cache.contains(s)) {
-		ret.second = cache.value(s);
+	ret.first = picture;
+	if (cache.contains(picture->filename) && !cache.value(picture->filename).isNull()) {
+		ret.second = cache.value(picture->filename);
 	} else {
 		int dim = defaultIconMetrics().sz_pic;
-		QImage p = QImage(s).scaled(dim, dim, Qt::KeepAspectRatio);
-		cache.insert(s, p);
+		QImage p = SHashedImage(picture).scaled(dim, dim, Qt::KeepAspectRatio);
+		cache.insert(picture->filename, p);
 		ret.second = p;
 	}
 	return ret;
@@ -49,14 +68,15 @@ void DivePictureModel::updateDivePictures()
 	}
 
 	stringPixmapCache.clear();
-	QStringList pictures;
+	SPictureList pictures;
 	FOR_EACH_PICTURE_NON_PTR(displayed_dive) {
 		stringPixmapCache[QString(picture->filename)].offsetSeconds = picture->offset.seconds;
-		pictures.push_back(QString(picture->filename));
+		pictures.push_back(picture);
 	}
 
-	Q_FOREACH (const SPixmap &pixmap, QtConcurrent::blockingMapped<SPixmapList>(pictures, scaleImages))
-		stringPixmapCache[pixmap.first].image = pixmap.second;
+	QList<SPixmap> list = QtConcurrent::blockingMapped(pictures, scaleImages);
+	Q_FOREACH (const SPixmap &pixmap, list)
+		stringPixmapCache[pixmap.first->filename].image = pixmap.second;
 
 	beginInsertRows(QModelIndex(), 0, numberOfPictures - 1);
 	endInsertRows();
@@ -121,5 +141,5 @@ DivePictureWidget::DivePictureWidget(QWidget *parent) : QListView(parent)
 void DivePictureWidget::doubleClicked(const QModelIndex &index)
 {
 	QString filePath = model()->data(index, Qt::DisplayPropertyRole).toString();
-	emit photoDoubleClicked(filePath);
+	emit photoDoubleClicked(localFilePath(filePath));
 }
diff --git a/qt-ui/divepicturewidget.h b/qt-ui/divepicturewidget.h
index aa524e1a6..e8104a1db 100644
--- a/qt-ui/divepicturewidget.h
+++ b/qt-ui/divepicturewidget.h
@@ -5,11 +5,18 @@
 #include <QListView>
 #include <QThread>
 
+typedef QPair<QString, QByteArray> SHashedFilename;
+
 struct PhotoHelper {
 	QImage image;
 	int offsetSeconds;
 };
 
+class SHashedImage : public QImage {
+public:
+	SHashedImage(struct picture *picture);
+};
+
 class DivePictureModel : public QAbstractTableModel {
 	Q_OBJECT
 public:
diff --git a/qt-ui/mainwindow.cpp b/qt-ui/mainwindow.cpp
index 7b204626c..8c3b44c48 100644
--- a/qt-ui/mainwindow.cpp
+++ b/qt-ui/mainwindow.cpp
@@ -37,6 +37,8 @@
 #endif
 #include <QNetworkProxy>
 #include <QUndoStack>
+#include <qthelper.h>
+#include <QtConcurrentRun>
 
 MainWindow *MainWindow::m_Instance = NULL;
 
@@ -50,6 +52,7 @@ MainWindow::MainWindow() : QMainWindow(),
 	Q_ASSERT_X(m_Instance == NULL, "MainWindow", "MainWindow recreated!");
 	m_Instance = this;
 	ui.setupUi(this);
+	read_hashes();
 	// Define the States of the Application Here, Currently the states are situations where the different
 	// widgets will change on the mainwindow.
 
@@ -201,6 +204,7 @@ MainWindow::MainWindow() : QMainWindow(),
 
 MainWindow::~MainWindow()
 {
+	write_hashes();
 	m_Instance = NULL;
 }
 
diff --git a/qthelper.cpp b/qthelper.cpp
index 4cedc5597..74c67d769 100644
--- a/qthelper.cpp
+++ b/qthelper.cpp
@@ -27,6 +27,11 @@
 #include <QUrlQuery>
 #include <QEventLoop>
 #include <QDateTime>
+#include <QSaveFile>
+#include <QDir>
+#include <QImageReader>
+#include <QtConcurrent>
+#include "divepicturewidget.h"
 
 #include <libxslt/documents.h>
 
@@ -780,3 +785,67 @@ extern "C" void reverseGeoLookup(degrees_t latitude, degrees_t longitude, uint32
 		ds->notes = add_to_string(ds->notes, "countrytag: %s", address.value("country").toString().toUtf8().data());
 	}
 }
+
+QHash<QString, QByteArray> hashOf;
+QHash<QByteArray, QString> localFilenameOf;
+
+extern "C" char * hashstring(char * filename)
+{
+	return hashOf[QString(filename)].toHex().data();
+}
+
+void read_hashes()
+{
+	QFile hashfile(QString(system_default_directory()).append("/hashes"));
+	if (hashfile.open(QIODevice::ReadOnly)) {
+		QDataStream stream(&hashfile);
+		stream >> localFilenameOf;
+		hashfile.close();
+	}
+}
+
+void write_hashes()
+{
+	QSaveFile hashfile(QString(system_default_directory()).append("/hashes"));
+	if (hashfile.open(QIODevice::WriteOnly)) {
+		QDataStream stream(&hashfile);
+		stream << localFilenameOf;
+		hashfile.commit();
+	} else {
+		qDebug() << "cannot open" << hashfile.fileName();
+	}
+}
+
+void add_hash(const QString filename, QByteArray hash)
+{
+	hashOf[filename] =  hash;
+	localFilenameOf[hash] = filename;
+}
+
+QByteArray hashFile(const QString filename)
+{
+	QCryptographicHash hash(QCryptographicHash::Sha1);
+	QFile imagefile(filename);
+	imagefile.open(QIODevice::ReadOnly);
+	hash.addData(&imagefile);
+	add_hash(filename, hash.result());
+	return hash.result();
+}
+
+QString localFilePath(const QString originalFilename)
+{
+	return localFilenameOf[hashOf[originalFilename]];
+}
+
+QString fileFromHash(char *hash)
+{
+	return localFilenameOf[QByteArray::fromHex(hash)];
+}
+
+void updateHash(struct picture *picture) {
+	QByteArray hash = hashFile(fileFromHash(picture->hash));
+	hashOf[QString(picture->filename)] = hash;
+	char *old = picture->hash;
+	picture->hash = strdup(hash.toHex());
+	free(old);
+}
diff --git a/qthelper.h b/qthelper.h
index a367a9dac..e164a41b6 100644
--- a/qthelper.h
+++ b/qthelper.h
@@ -7,6 +7,7 @@
 #include "dive.h"
 #include "divelist.h"
 #include <QTranslator>
+#include <QDir>
 
 // global pointers for our translation
 extern QTranslator *qtTranslator, *ssrfTranslator;
@@ -16,5 +17,11 @@ bool gpsHasChanged(struct dive *dive, struct dive *master, const QString &gps_te
 extern "C" const char *printGPSCoords(int lat, int lon);
 QList<int> getDivesInTrip(dive_trip_t *trip);
 QString gasToStr(struct gasmix gas);
-
+void read_hashes();
+void write_hashes();
+void updateHash(struct picture *picture);
+QByteArray hashFile(const QString filename);
+void add_hash(const QString filename, QByteArray &hash);
+QString localFilePath(const QString originalFilename);
+QString fileFromHash(char *hash);
 #endif // QTHELPER_H
diff --git a/save-git.c b/save-git.c
index 0125f64d7..a7b51446a 100644
--- a/save-git.c
+++ b/save-git.c
@@ -585,6 +585,7 @@ static int save_one_picture(git_repository *repo, struct dir *dir, struct pictur
 
 	show_utf8(&buf, "filename ", pic->filename, "\n");
 	show_gps(&buf, pic->latitude, pic->longitude);
+	show_utf8(&buf, "hash ", pic->hash, "\n");
 
 	/* Picture loading will load even negative offsets.. */
 	if (offset < 0) {
diff --git a/save-xml.c b/save-xml.c
index 8366f87ff..c68b5b633 100644
--- a/save-xml.c
+++ b/save-xml.c
@@ -359,6 +359,8 @@ static void save_dc(struct membuffer *b, struct dive *dive, struct divecomputer
 	put_format(b, "  </divecomputer>\n");
 }
 
+extern char * hashstring(char * filename);
+
 static void save_picture(struct membuffer *b, struct picture *pic)
 {
 	put_string(b, "  <picture filename='");
@@ -377,6 +379,9 @@ static void save_picture(struct membuffer *b, struct picture *pic)
 		put_degrees(b, pic->latitude, " gps='", " ");
 		put_degrees(b, pic->longitude, "", "'");
 	}
+	if (hashstring(pic->filename))
+		put_format(b, " hash='%s'", hashstring(pic->filename));
+
 	put_string(b, "/>\n");
 }