It's not layers. I have no idea how to code it, but I ahve an idea... sort of.
The coder places the new image in the code and sets the left and right up and down placement of the image over the original. The only problem is that when you do that, you can see the new image over all the other pet images when you flip throught he profile pets.
It's called an overlay. Basically a DIV box is placed over the area of the original pet image and scaled down to just slightly larger than the new image. The new image is then added using the normal <img src=url here> code. Making a DIV overlay is actually pretty simple, just google DIV codes and trial and error will tell you where to place it in terms of px from the top and left.
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Normal User
Normal User
Normal User