diff --git a/Base/include/FasTC/Image.h b/Base/include/FasTC/Image.h
index b09b6cb..2f1997b 100644
--- a/Base/include/FasTC/Image.h
+++ b/Base/include/FasTC/Image.h
@@ -97,6 +97,8 @@ namespace FasTC {
     double ComputePSNR(Image<PixelType> *other);
     double ComputeSSIM(Image<PixelType> *other);
 
+    Image<PixelType> Diff(Image<PixelType> *other);
+
     double ComputeEntropy();
     double ComputeMeanLocalEntropy();
     
diff --git a/Base/src/Image.cpp b/Base/src/Image.cpp
index 8700517..405cb99 100644
--- a/Base/src/Image.cpp
+++ b/Base/src/Image.cpp
@@ -48,6 +48,7 @@
 #include <cstdio>
 #include <cstring>
 #include <cassert>
+#include <iostream>
 
 #define _USE_MATH_DEFINES
 #include <cmath>
@@ -66,6 +67,29 @@ static inline T Clamp(const T &v, const T &a, const T &b) {
   return ::std::min(::std::max(a, v), b);
 }
 
+template<typename T> inline T PixelAbs(const T &a);
+template<> inline FasTC::IPixel PixelAbs<FasTC::IPixel>(const FasTC::IPixel &p) {
+  return FasTC::IPixel(fabs(p[0]));
+}
+
+template<> inline FasTC::Pixel PixelAbs<FasTC::Pixel>(const FasTC::Pixel &p) {
+  FasTC::Pixel result = p;
+  if (result.R() < 0) { result.R() = -result.R(); }
+  if (result.G() < 0) { result.G() = -result.G(); }
+  if (result.B() < 0) { result.B() = -result.B(); }
+  if (result.A() < 0) { result.A() = -result.A(); }
+  return result;
+}
+
+template<> inline FasTC::Color PixelAbs<FasTC::Color>(const FasTC::Color &p) {
+  FasTC::Color result = p;
+  if (result.R() < 0) { result.R() = -result.R(); }
+  if (result.G() < 0) { result.G() = -result.G(); }
+  if (result.B() < 0) { result.B() = -result.B(); }
+  if (result.A() < 0) { result.A() = -result.A(); }
+  return result;
+}
+
 // wtf
 #ifdef _MSC_VER
 template<typename T> T log2(T x) { return static_cast<T>(log((long double)x) / log(2.0)); }
@@ -174,6 +198,35 @@ const PixelType & Image<PixelType>::operator()(uint32 i, uint32 j) const {
   return m_Pixels[j * GetWidth() + i];
 }
 
+template<typename PixelType>
+Image<PixelType> Image<PixelType>::Diff(Image<PixelType> *other) {
+  if (!other) {
+    std::cerr << "Image::Diff - ERROR: other == null" << std::endl;
+    assert(false);
+  }
+
+  if (GetWidth() != other->GetWidth() ||
+      GetHeight() != other->GetHeight()) {
+    std::cerr << "Image::Diff - ERROR: Images differ in dimension" << std::endl;
+    assert(false);
+    return *this;
+  }
+
+  this->ComputePixels();
+  other->ComputePixels();
+
+  Image<PixelType> result(GetWidth(), GetHeight());
+  for (int j = 0; j < GetHeight(); ++j) {
+    for (int i = 0; i < GetWidth(); ++i) {
+      result(i, j) = PixelAbs((*this)(i, j) - (*other)(i, j));
+      result(i, j).MakeOpaque();
+    }
+  }
+
+  // !SPEED! We do an unnecessary copy here...
+  return result;
+}
+
 template<typename PixelType>
 double Image<PixelType>::ComputePSNR(Image<PixelType> *other) {
   if(!other)
diff --git a/CLTool/src/compare.cpp b/CLTool/src/compare.cpp
index 4ed6f79..039cf7a 100644
--- a/CLTool/src/compare.cpp
+++ b/CLTool/src/compare.cpp
@@ -47,6 +47,7 @@
 #include <cstdlib>
 #include <cstdio>
 #include <cstring>
+#include <ctime>
 #include <iostream>
 #include <fstream>
 #ifdef _MSC_VER
@@ -59,27 +60,67 @@
 #include "FasTC/TexComp.h"
 #include "FasTC/ThreadSafeStreambuf.h"
 
+static void PrintUsageAndExit() {
+  fprintf(stderr, "Usage: compare [-d] <img1> <img2>\n");
+  exit(1);
+}
+
+void gen_random(char *s, const int len) {
+  static const char alphanum[] =
+  "0123456789"
+  "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+  "abcdefghijklmnopqrstuvwxyz";
+
+  srand(time(NULL));
+  for (int i = 0; i < len; ++i) {
+    s[i] = alphanum[rand() % (sizeof(alphanum) - 1)];
+  }
+
+  s[len] = 0;
+}
+
 int main(int argc, char **argv) {
-  if(argc != 3) {
-    fprintf(stderr, "Usage: compare <img1> <img2>\n");
-    return 1;
+  if(argc != 3 && argc != 4) {
+    PrintUsageAndExit();
   }
 
-  ImageFile img1f (argv[1]);
+  bool diff_images = false;
+  int arg = 1;
+  if (strncmp(argv[arg], "-d", 2) == 0) {
+    diff_images = true;
+    arg++;
+  }
+
+  ImageFile img1f (argv[arg]);
   if(!img1f.Load()) {
-    fprintf(stderr, "Error loading file: %s\n", argv[1]);
+    fprintf(stderr, "Error loading file: %s\n", argv[arg]);
     return 1;
   }
+  arg++;
 
-  ImageFile img2f (argv[2]);
+  ImageFile img2f (argv[arg]);
   if(!img2f.Load()) {
-    fprintf(stderr, "Error loading file: %s\n", argv[2]);
+    fprintf(stderr, "Error loading file: %s\n", argv[arg]);
     return 1;
   }
+  arg++;
 
   FasTC::Image<> &img1 = *img1f.GetImage();
   FasTC::Image<> &img2 = *img2f.GetImage();
 
+  if (diff_images) {
+    FasTC::Image<> diff = img1.Diff(&img2);
+
+    char fname_buf [5 + 16 + 4]; // "diff-" + hash + ".png"
+    strncat(fname_buf, "diff-", 5);
+    gen_random(fname_buf + 5, 16);
+    strncat(fname_buf + 5 + 16, ".png", 4);
+
+    EImageFileFormat fmt = ImageFile::DetectFileFormat(fname_buf);
+    ImageFile cImgFile (fname_buf, fmt, diff);
+    cImgFile.Write();
+  }
+
   double PSNR = img1.ComputePSNR(&img2);
   if(PSNR > 0.0) {
     fprintf(stdout, "PSNR: %.3f\n", PSNR);