XnView is an free image viewer and graphical file converter. It can import close to 400 different graphic formats and can export around 40 different formats. XnView offers users the ability to apply filters, effects, resize images and modify number of colors as well. It also supports batch processing, allowing the user to resize a group of images at once. Best of all, XnView can be run from a USB device.
License: Freeware (for non commercial use)
Authors Website: http://www.xnview.com/en/
Installing XnView to a USB device: