You're probably familiar with CAPTCHAs -- images of letters and numbers that websites use to verify that users are people, not automated programs. The Tumblr blog CAPTCHArt is filled with user-submitted cartoons inspired by the phrases found in CAPTCHAs.
Link via Urlesque | Previously: Topological and Other Strange CAPTCHAs
Most CAPTCHAs don't make any sense to me, the only ones which come close are the ones used in Blogger (when commenting), they usually have random phrases in them.