Spammers have employed this technique since roughly about the time they started sending images. See here for some examples: http://www.jgc.org/tsc.html http://

Spammers have employed this technique since roughly about the time they started sending images. See here for some examples: http://www.jgc.org/tsc.html http://www.jgc.org/tsc.html Also, real OCR is too expensive to do at the volumes of mail being sent today. Gmail is likely using an OCR-esque technique that has lower precision but is much faster to process a given image.