Gimp (Image Manipulation Program--like Photoshop)

piZab (free editing program that allows you to speech bubbles and other enhancements to photos)

Fotobabble (allows you to add voice to your photos)

Jing (take snapshots of images on your computer screen)

Morgue File (free photos you can use for class projects)

Wikipedia Commons Images (free photo site powered by Wikipedia)

Ken Thomas (public domain pictures of nature)

ookaboo (public domain and creative commons licensed images)

copyright friendly (links to lots of sites with public domain and creative commons images)

Free Digital Images (free stock photos)

Wylio (creative commons images)