Almost every semester, we offer Media Matter sessions for Photoshop. Sign up at media.cnu.edu.
Free/Open source photo editing software:
Paint.NET is an image and photo editing software free for download onto any Windows computer.
Adobe's Photoshop is the preeminent photo editing software available today. Although you can create images from scratch, it is mainly used for photo editing. If you want to create images from scratch, Adobe's Illustrator is the better way to go. With Photoshop, you can do almost anything imaginable. Some of the many tasks you can do with Photoshop: change an existing picture, animate, edit video, prepare images for the web, create an automated work flow and so much more.
The Media Center has Adobe Creative Suite CC on all of our Macs and in the Editing Suites.