Here is my experience of what I've done in similar situations, I hope this helps.
First, regarding the initial part of your question, you have not way of reading the parameters of the method didFinishPickingMediaWithInfo to determine what UIImageView was the one pressed. But you can easily keep a reference to the lastPressedImageView in you view controller and keep it as simply as reading this variable once you receive didFinishPickingMediaWithInfo.
Regarding the second part of your question I recommend you reading / researching about AFNetworking which is a really powerful and easy to learn library for networking in iOS. You'd need to add your own logic to create the requests and send them, as well as for controlling possible errors, but this lib will help you to concentrate on logic instead of low-level networking concerns.