1 Free Image Editors

Obviously there are a large number of commercial image manipulation packages available. However, there are free image viewers that you might find very valuable, including:

2 Free Image Viewers and Converters

There are also some free image viewers that you might find very valuable, including:

3 Visual Content

There are a variety of sites containing visual content. You are responsible for using them responsibly and legally.

The Harvard University library also maintains a list of sites.