Transloadit offers media upload, modification, and storage as a service for developers who need that functionality (or, as Transloadit's homepage puts it, "geeks who run web or mobile applications") but don't want to worry about it themselves. There aren't too many moving parts to it, but they're ones a lot of applications make use of. The Transloadit API's main functions include: file upload, image resizing, video file encoding, image thumbnail creations, and file storage on Amazon S3.
If you are building an image sharing service or a social network mashup, it's likely that you will want to incorporate face-tagging in your images. Maybe you'd like to go a step further and automatically detect faces in an image, similar to Apple's iPhoto. A Romanian developer has developed an API to help detect faces in images and return the box coordinates so that you can build any kind of app you want.
Facebook has rewarded a 10 year-old boy from Finland with a $10,000 bounty for discovering an authentication-related vulnerability in the Instagram API that could have enabled a hacker to delete comments of any user on the popular social photo sharing service even without an Instagram account.