Anti-spam technology companies are now reporting that about half of all Unsolicited Bulk Email (UBE) is arriving in the form of image spam. Image spam makes use of embedded image files (generally in a .gif or .jpeg format) to deliver its message or malware.
Image spam is used – and rapidly on the rise – because of the success spammers have had in bypassing spam filters with it. Standard spam filters, like those that use Bayesian and heuristic methods, are unable to “read” image files and therefore cannot perform any text analysis on the content. While text analysis is not the sole method used by most anti-spam technologies, it remains heavily relied upon in conjunction with other methods.