GIMP is an abbreviation for GNU Image Manipulator Program. This is a free and open source raster image program that can replace Photoshop for many users. The GIMP program is a little buggy and it natively lacks a few features I would like to see implemented, but overall, it can complete the advanced image manipulation tasks including color channels, layers, conversions, and more.
GIMP is installed on many Linux distros by default, but if you have a lightweight distribution, you will probably need to install it yourself in the software manager or terminal. GIMP is a great program for anyone that needs to edit images including converting images, cropping, changing image size, etc. The program is also capable of automation, though it is a little more complicated. Even the more advanced image editor will be able to use GIMP. The power of the program is that it can be extended with plugins to provide more advanced features, so whether you are an image novice or an advanced photograph editor, GIMP is a must have for any Linux installation.