If the iPhone is supervised, when the device is first supervised, there's a checkbox to allow syncing with other computers. Was this done or is the problem you're running into because this wasn't done?
Does the user have iCloud and iPhoto library enabled? If so then the originals should be in iCloud after a full icloud backup. If not, maybe you can get the device connected to the mac which originally supervised it and then you should be able to sync it with iTunes on that original mac and get at the photos that way.
