If your photo was in a challenge at the time it ended it might have earned an achievement.

When you press on such a photo it will show the achievements which can be anything from the 'Top Photographer' to the level in which you placed.

These achievements are counted at the top of each photo and show at the bottom of it when opened.

It's important to note that the count is done per achievement and not the number of challenges in which it has earned them.