Using GIMP.
Nose Flip
I use the Gimp for image comparisons related to Henry Holiday's illustrations to Lewis Carroll's The Hunting of the Snark (1876). Most comparisons are static, but here a little animation done with the Gimp helps to show how Henry Holiday played with art from other artists. When illustrating the book, Henry Holiday didn't just copy art. This example shows that he had discovered, that you can flip a "nose" in the etching The Image Breakers (c. 1567) by Marcus Gheeraerts the Elder in a way that it turns into another nose. And that flipped nose then became the nose of the "Banker" in Carroll's tragicomedy.





Sounds intriguing. When you say comparison, you use GIMP to highlight what is common? That is what the animated example is showing us?
Basically, this is about a skillful pictorial allusion by Henry Holiday in one of his nine illustrations to Lewis Carroll's The Hunting of the Snark to a 16th century etching.
As for the side-by-side comparison, the easy part was to squeeze Gheeraerts's etching (right image, source: a vectorized reproduction) horizontally a bit. I didn't use GIMP for any any highlighting.
The more interesting part is How Henry Holiday played with the nose in Gheeraerts' etching. I used the GIMP animation package to show how Henry Holiday must have discovered what happens to the nose if you mirror it along a horizontal axis: It turns into another nose with a different shape. (Gheeraerts probably had not intended that.)
Very practical. Thank you very much for sharing ^_^