Screenshot viewer is a mod that allows you to see the screenshots that you have taken while you were gaming! (including the accidental ones you took when you where trying to press F3).
It comes with a great GUI and an in-game configuration thanks to CatConfigMC, a library I myself developped.
Here are two screenshots of the in-game GUI:
If you want to see in detail one of your screenshots, or just go through them, you can click on one to enlarge it and scroll or click on the buttons on the left and right to go to the next one or the previous one.
Finally, you can access this screenshots management screen by clicking on a button on the title screen or in the pause menu, or by configuring a key binding.
Hope you will enjoy the mod!