When my dog was a few months old, he definitely noticed himself in the mirror and he was curious until he looked behind it. As soon as he realized there was no dog behind the mirror, he has never looked into that mirror again. He just walked away from it and whenever he passes it now, which is about 60 times a day, he doesn't even turn his head in that direction. That's the part I think is weird, not that he recognized the image of a dog, but that he never looked into the mirror again after realizing that it was just an image.