Alternative / Free / Open source image editor: GIMP

GIMP (GNU Image Manipulation Program) is an open source graphic software suitable for such tasks as photo retouching, image composition and authoring. It is a powerful software with capabilities not found in any other free software product. It can be used as a simple paint program, an expert-quality photo-retouching program, an online batch-processing system, a mass production image renderer, or an image-format converter.


It is multi-platform supported including Linux, Microsoft Windows and Mac OS X.

Pros
Multiplatform
Powerful image editing tools
Lots of interface tweaks to make it newbie friendly
Single-window mode
Powerful free image editing program

Cons
Can't view multiple items in single-window mode
Not many included automated features