Gimp
Configuring Software - Image viewer and editor
Most windows users are used to the Microsoft Photo Viewer or Image and Fax viewer that come with Windows and Microsoft Office. A similar application for Linux is a nice lightweight application called Ristretto.
$ sudo emerge -av ristretto
Once installed, you may want to go into the preferences and check the box for "Open entire folder at startup" so you can cycle through all of the images in a folder by default.
One of the most popular image editing applications, and a target of software piracy, is Adobe Photoshop. Many people are infected with trojans and malware trying various hacks in order to run Photoshop. No need! The open-source solution, GIMP (GNU Image Manupulation Program) has the same features as Photoshop for most users, and is totally free.
$ sudo emerge -av gimp
As always, before the emerge, check your USE flags and ensure you have your desired flags set.