1. A method to be performed using a computer, the method comprising: collecting a set of spam messages; extracting images from the spam messages; analyzing the extracted images by comparing the extracted images to one another to identify those generated using a same image template; forming clusters of related spam messages, each of the cluster of related spam messages comprising spam messages from the set of spam messages having images generated using a same image template; and identifying sources of spam messages in each of the clusters of related spam messages.