The requirement for using the User Generated Photo action property is documented as:
"The User Generated Photos action property can only be used if the photos are original and taken by a user with an actual camera."
Is there any guidance available as to how strictly this is to be enforced?
Would a mobile app have to disable the selection of an image from the phone's gallery (as we cannot be sure that the selected image in this case is original or indeed a camera photograph)
What level of processing of the photograph is acceptable? I presume filters and frames are OK. How about overlaid text or other graphics? How about generating a larger image with the original photo as a smaller part of it?
You should let the user upload what they want, but just make it clear in your Terms and Conditions what the requirements for a photo are. Filters, cropping, etc should be fine and the photo will still be original.
You should put in place a moderation tool so you can easily delete / hide photos that don't comply with the Terms (i.e. in an admin section), and allow users to 'report' images. It's extra work but it means you have overall control of the photos that user's upload.