Hidden Disney Characters in Disney Movies
At the pet shop in "101 Dalmatians" all of the dogs in the window are puppies except for this familiar dog in the corner. The dog is Peg from the classic Disney film "Lady and the Tramp"
In the film "Treasure Planet", on the shelf on the far left side a familiar character can be seen. It's Stitch from "Lilo and Stitch", which was released the same year.
Of all of the Disney/Pixar movies, "Finding Nemo" probably has the most references to other films. Like this shot of Luigi from "Cars", a film that was still in production at the time.