Spammers hide messages in image files to escape detection. Image spam accounts for 30 percent of all spam and approximately one in every four messages circulating on the Internet. Spammers are using advanced mathematical and graphical techniques like random modification of image pixels and dynamic construction of images from multiple components to bypass spam filtering tools. Traditional anti-spam software depends on content filtering techniques such as keyword filtering and Bayesian analysis to detect spam. Even the technology used to recognize characters from images, Optical Character Recognition (OCR) is not effective on today’s image spam.”]
Source: https://www.darkreading.com/attacks-breaches/secure-computing-targets-spam