FuzzyOcr is a plugin for SpamAssassin which scans image attachments for
spam keywords, using an Optical Character Recognition program.

This plugin can be used to detect spam that puts all the real spam
content in an attached image. The mail itself only random text and
random html, without any URLs or identifiable information.

It is also able to do approximate matches on words, so errors in
recognition or attempts to obfuscate the text inside the image will not
cause the detection to fail.