The issue is that “Photos” do not show up on the Apple TV under “My Computer”, I see it too consistently. What I found that fixes it temporarily, is this:
1. In iTunes, go to “File->Home Sharing->Choose Photos to Share with Apple TV…” (That is the name on iTunes 12.3.1)
2. Then turn on or off an album. (It did this for the Apple TV 2, 3 and the new ATV 4).
3. Then hit Apply and close that window.
4. Then it starts showing up on the Apple TV.
So, every time I restart iTunes, I go in there and just have an album that I don’t care about and turn it on if it was off, and off if it was on.
This has helped some people who didn’t get it fixed by rebooting everything etc.