I get what you mean and where you're coming from but Persona's concept is still pretty different. People do post images of things they think will represent them, but that doesn't say much about who they are. Anyone can post photographs and upload them, but it's the meaning behind the photograph that creates a bond. For example: If I take a picture of Hot Cheetos and post it on Tumblr or Pinterest, people who view it will normally associate me being interested or liking Hot Cheetos. But the truth is, nobody cares because millions of people like Hot Cheetos as well. On Persona, we focus purely on things around you that make you who you are; when you post an image, we ask you "what does this mean to you?" If I were to post Hot cheetos on Persona, I'd say "Hot cheetos are musthaves for me when I'm programming." That might not mean everything to everyone, but for the people that can really relate to it, it becomes an intimate connection. It's all the small idiosyncrasies that describe who you are.
It's difficult to fully depict the differences because all apps of similar nature have some sort of overlapping. For example, most people still can't fully explain why Path is so different from Facebook. I use Path but I can't seem to tell people why it's different, aside from the fact that you have a private network vs a public one. If you're asked, "How is Tumblr different from Pinterest?", you'd have just as hard a time answering.
From what I see, Tumblr and Pinterest users don't answer the question of why they post something. I use Tumblr for the sake of killing time and just seeing what pops up and reblog and share things that I think are cool. When I post on Tumblr, I don't think "how does this relate to my life?" I used to ride a motorcycle so I like reblogging nice bikes on Tumblr but that doesn't mean anything to anyone. It doesn't tell the story of how I saved up money to get my first motorcycle, the first time I dropped my bike, or how upset my parents were with me buying it. For me, Tumblr is just a great, mindless way to kill time.
Pinterest for me, is a better way of organizing my bookmarks. I share links and photos from other sites because they interest me. Like with Tumblr, I don't necessarily stop to think why I'm putting a photo to my board- it's just a great way to visualize all the things that interest me and my friends on one page. I have a section for recipes, a section for funny stuff, another section for just cool arts and craft stuff. I browse Pinterest by categories just to find something cool/interesting that I want to go back to afterwards. It's a great service because I've use my browser bookmarking feature a lot less now.
Here's a question I asked myself for Tumblr and Pinterest: "Can you figure out what your friend would want as a practical gift for her birthday?" I wouldn't be able to; my friend shares everything from recipes to pictures of dogs to wedding gowns. But truth is- she's doesn't cook, is allergic to dogs, and is already married. It wouldn't make sense to buy her a dog or kitchenware right? Knowing that she doesn't cook, that she's allergic to dogs would be the prime examples of the kind of personal understanding you'll have of someone on Persona. It's not about what you're liking, reblogging or upvoting. It's about the real side of you, the one where you parents and only close friends know about.
Thanks for the feedback!