Image Editing Toolset for Mac

All of the following are free and available on the Mac:

• Grab - Awesome tool for taking snapshots of on screen material.
• iPhoto - Decent~ish for cropping.
• Preview - Pretty good for cropping. You can follow the instructions given here. Hint: Select what should remain then press "cmd+k" to crop out the rest.
• Gimp
  • Great for smudging out unwanted portions of existing images.
  • Converting regular icons into those that look disabled