I'm looking to create a mobile app that aggregates information from other apps. For example, every time someone posts an image, comment, post etc using other apps on their mobile like Facebook, Twitter, Instagram, my app would grab that content, or at the very least a unique ID that references that content, an store it in a log.
The app would be 100% opt-in, and transparent. I'm not sure how to best approach this, or if it is even possible, whether something could be done at a low-level on the device, or if it would even be possible using API's (although I don't know if I could subscribe to such events, and even if I could, how would the app know when the post/picture was uploaded from the phone as opposed to a desktop).