The Scourge of Image Spam

E-mail solicitations that use graphical images of text to avoid filters are not new. Recently, however, they became more sophisticated and account for roughly 40 percent of spam today.

The spammer's challenge, then, is to deliver something that the filter hasn't yet learned is spam. Eventually, the filter incorporates the new derivations into its list of spammy traits. Then the spammer changes convention again, and on and on.

Spammers have made image spam really effective by using not just one but multiple filter-thwarting techniques. Some confuse optical character recognition filters, some automatically alter images to create randomness, and some even buffer against defenses that don't yet exist but that spammers anticipate will be built in response to image spam.