Awww what an adorable picture of Mickey admiring himself!!!

About your question, I have heard that humans are the only species (maybe monkeys too??) that can identify a mirror as a reflection of themselves right off the bat. I know it took my brother's cats the longest time to figure out that it wasn't another cat in there, and I wonder if Mickey is seeing another pup and he just wants to play!! It could be, also, that he associates seeing an image of another pup (the front door) with going out. It's hard to say, but he's still a very young pup & is learning tons of stuff about his surroundings everyday, and it might take him a little while until he figures it out.