If you are presenting to or writing for a group external to UNC, please check with them regarding fair use policies. Many commercial uses of images (uses where you make money) are not allowed under Fair Use guidelines.
There are many different programs that can be used for image editing. Here are a few that the MDS team recommends:
Adobe products are available to UNC students for free through UNC ITS Software Distribution. If you're a first time Photoshop user, try out our Introduction to Photoshop online tutorial in order to learn the basics.