Is there a command line program or library that turns image files into ASCII art?

Is there such a thing? I would like to use it in a Ruby program.

Try this http://csl.sublevel3.org/jp2a/

Also, there may be some stuff with Imagemagick

There's jp2a which converts jpegs. It's pretty cool!

Just to add another solution. There is also AAlib. http://aa-project.sourceforge.net/aalib/

You should be able to read in the output or pipe into a file for reading.