Sometimes you have a photo which you took, say, in 16 by 9 proportion, and you want to print it on, say, 4 by 3 paper, without cropping. Or maybe you want to use it as a wallpaper on a screen of a different proportion. For that, there's letterboxing: adding a border on two sides to adjust the proportions. This app does that. Photo Letterboxer is basically a universal filter.