xli (X11 Image Loading Utility)

This utility will view several types of images under X11, or load
images onto the X11 root window. Supported image formats include
GIF, JPEG, JFIF, Faces, PNG, PPM and friends, XPM, and XWUD.

A variety of options are available to modify images prior to viewing.
These options include clipping, dithering, depth reduction, zoom
(either X or Y axis independently or both at once), brightening or
darkening, input gamma correction, and image merging.  When applicable,
these options are done automatically (eg. a color image to be displayed
on a monochrome screen will be dithered automatically). A utility (xlito)
is provided that allows these viewing options to be appended to the image
files.