Its on data/petface/128 and data/petface/round (round folder have 2 pic for each pet).
If you edit them, theres no problem aslong as you save with same name (overwrite), and same extension.
-EDIT- Just saw your post. In that case, you should look at eudbook.ini, search for copper rhino, and take out the ID (1071xxx). Then go to ani/PetFace.ani and search for that ID, example:
Code:
[Face1079662]
FrameAmount=6
Frame0=data/PetFace/128/Face1071660.dds
Frame1=data/PetFace/128/Face1071660.dds
Frame2=data/PetFace/round/PetIcon-R1079660.dds
Frame3=data/PetFace/round/PetIcon-R1079661.dds
Frame4=data/PetFace/round/PetIcon-R1079660.dds
Frame5=data/PetFace/round/PetIcon-R1079661.dds
Then just follow those directory's and see if the files are there.