ImageMagick

ImageMagick is a program that is capable of reading, converting, and representing images in a wide variety of formats, thanks to the large amount of libraries that it contains.

You can use ImageMagick to crop your images, add effects, combine text and polygons, add rotations, etc.

The program supports almost 100 different image formats, from the most popular (TIFF, JPG, PNG, GIF, BMP, PDF) to some more esoteric.

ImageMagick also works as an image converter.

Not only that, but the application is totally free and distributed with open-source code in case you want to alter and improve it.