Spammers tend to use more advanced spam methods to avoid the dreaded spam filters that become better and better. I would like to present some examples from my personal mail folder and analyze the latest image spam trends. Many spam filters concentrate their efforts on blacklists and the text that the mail contains. Spam that is not caught immediately will be caught in the future if the user marks that mail as spam. Language and keyword filters and white lists do their part and reduce spam and false positives.
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 is send in spam mails. 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.
Another option to create a unique image would be to use colors that look the same to the human eye but differ for the computer. Randomizing the process creates unique images as well.
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 such a spam mail is seemingly 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.
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