Image spam on the other hand is on the rise because of several new spam techniques that make it pretty hard for the filters to automatically recognize spam.

The left image is an example of a typical image that appears in spam emails. The following techniques were used in this mail to bypass the spam filter. The first obvious element are random pixels that overshadow some part of the image. This is done to create random images which can bypass spam filters even though an image with the same information arrived before in your mailbox.

Other options to achieve a similar effect include using colors that look the same to the human eye but not to the computer, and randomizing processes to create unique images.

Some spammers use different layers for a set amount of pixels which makes it incredibly hard to to use hash values to determine spam images.

The last aspect of image based spam emails is random text that is copied before or – more often – after the image. The text itself has nothing to do with the intention of the spammer. It is solely used to simulate a normal mail with a set amount of neutral and positive words.

The image on the left shows another image that is often used to bypass spam filters. It uses random colors much like the previous image used random pixels that made the image unique.