Android :: Photo Hash Changes After Upload

I've written an app that syncs social network photos with your phone's contact photos. It works great. However, I have an option that lets the user skip any contacts that already have a photo added. This works great until the phone (I assume) syncs up the photo from the social network with Google Contacts.

I use a hash of the pic to track if the picture is one from my sync app or one that the user has added themselves. So, if Google Contacts changes the format of the pic, then the hash will change and my method is no good!