During one of my PHP security sessions, I was asked about “calculation captchas”. These look like this: and the Turing test (if you want to call it that) is solving the task in the picture.
But wait, isn’t it the main function of a computer to perform calculations? So how can this be "Completely Automatted Public Turing test to tell Computers and Humans Apart?
Just for shits and giggles, I downloaded 100 of these little images from the site that I saw them on, and fired up gocr. I piped the results into bc and voilá: