Once a photo has won a challenge it can't be used again in future challenges.
This includes any revised versions with a crop, flip or hue changes.
The only unique case in which this is allowed: a photo is taking part in several active challenges and wins one of them.
This is the only time where the photo will not be removed from the challenges.
Note: If you swap the photo out of the challenge after the win, you will not be able to bring it back in.