One of the difficulties that spam filters have, is the identifying of SPAM with out text.
If there is a text base d message, the filters can analyze the message content and decide of this is indeed SPAM or a valid piece of communication.
When that same message is converted to an image, such as a photograph, it is harder to decypher.
A company called CommTouch has developed a potential solution for ths type of SPAM. They are able to identify the and interpret the grahic message and perform an analysis on that.
THis may reverse a curent trend in the use of image based SPAM.