The second information which I see having potential is the EXIF of the pics, the off pixels and other identifying data of the camera (flare, blur, watermark), a

The second information which I see having potential is the EXIF of the pics, the off pixels and other identifying data of the camera (flare, blur, watermark), artificially introduced or not. Not only it proves who we with whom at the same time. It also links profiles. You can create a whole new identity; but if you didn't throw away all your phones and cameras, then Facebook can link the profiles. Or if you sell something on Craigslist and upload on Snapchat with the same camera: It's tied to your identity.