There is a huge variety of software for manipulating images in various ways. Much of this software can be grouped under the heading image processing software, and the bulk of this reference is concerned with that group.
Another very important category is what we call image editing software. This group includes painting programs, graphic art packages and so on. They are often useful in conjunction with image processing software packages, in situations where direct immediate interaction with an image is the easiest way of achieving something. For instance, if a region of an image is to be masked out for subsequent image processing, it may be easiest to create the mask using an art package by directly drawing on top of the original image. The mask used in the description of the AND operator was created this way for instance. Art packages also often allow the user to move sections of the images around and brighten or darken selected regions interactively. Few dedicated image processing packages offer the same flexibility and ease of use in this respect.