Having the user set the background image of an imageView

I'm a programming newbie, although not completely programmatically incompetent, so sorry if I appear oblivious. I have a functioning image view with an image I have, and it responds to the users events. However, I need the user to be able to set a photo from their camera roll to be the background image for my imageview. I think I have the code for a user to scroll through (and select?) from their library, the only thing I wasn't sure about was how to link buttons to load either the camera roll or the image view after a picture has been selected.

I really appreciate your help.