The Swiss army knife of DOS viewers. Does almost everything, but a bit intimidating for newcomers. User interface is much improved over early versions, but still awkward in places. Requires 386 or better. A well-done viewer and image converter for many image formats.
Installation is simple, and the on-line documentation is very good.
JPEG loading is a bit slower than the above viewers, though. Current version is 3.1f. Views JPEG and half a dozen other image formats. Easy to use, very easy to install. Only moderately fast, but it has lots of options.