I guess the hard part would be aligning the images. But maybe you could do a series of resize and rotations and check for minimum difference?

From perldoc Imager::Filters

 Image Difference

  You can create a new image that is the difference 
  between 2 other images.
      my $diff = $img->difference(other=>$other_img);
  For each pixel in $img that is different to the pixel in
  $other_img, the pixel from $other_img is given, otherwise
  the pixel is transparent black.

       This can be used for debugging image differences  ("Where are t
+hey different?"), and for optimizing animated   GIFs.

       Note that $img and $other_img must have the same               
+ number of channels.  The width and heigh of $diff will be the minimu
+m of each of the width and height of $img and
       $other_img.
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