An article by Virginia Morell in the latest National Geographic discusses an interesting test of dog intelligence. A dog was shown a series of color photographs depicting dog-toys. After seeing image, the dog then had to go into a nearby room and retrieve the toy depicted in the photograph from among a stack of various toys and photographs. The dog brought back either the toy depicted or a photograph of it every time.
The fact that a dog can decode a photograph is pretty amazing. When asked what the photograph was, the dog essentially thought to itself (at least part of the time), "it's not the photograph that's important but the thing in the photo." It takes a certain amount of interpretive power to reach that point, and I doubt that any animal besides dogs or humans could do so. Humans are probably the only species that could spend 150 years retreating from it.