I'm not familiar with how an Apple TV works since I don't own one, but I know that the Synology runs a standard DLNA server for all of that stuff, as well as being an SMB file share, so if Apple TV supports showing media from either of those things, it should theoretically just work. I know that I can directly use my Playstation 3 or my Xbox to display photos and videos that are stored on the NAS, no problem.

I'm not sure whether there is a super-easy path for copying the photos and videos from the mobile devices onto the NAS. For me, the path always involves copying those things onto my PC first, then copying those things up to the NAS. Not difficult, but it's two steps rather than one.

Synology has some mobile apps like Photo Station and Video Station which run on the mobile devices, I wonder if those will support directly uploading those things to the NAS from the phone? I never tried.