There are numerous programs for image editing. A list of links can be found below.
To learn image editing, a good idea is to look for instructional videos online. An example is this tutorial on how to remove a background with Gimp.
Installable Image Editors
- Photoshop - professional, expensive
- Photoshop Elements - small brother of Photoshop
- GIMP - best free alternative
- Paint.net - free and simpler than GIMP
- Inkscape - a free editor for vector graphics