sdl_img

A "simple" open source image viewer based on stb_image.h (with the suggested animated GIF API extension) and SDL2.

It's "simple" in that it would work fine as a drop in replacement for most people since all the normal/expected behavior is there, but it has tons of extra and unique features for power users, especially on Linux/Unix and if you're comfortable with the terminal.

You can read more details about it and see the source code on Github