article_snippet: others had detained .
article_snippet: ISIS and Al Qaeda are hiding messages to ISIS and Al Qaeda followers in digitally-altered eBay photos and even pornography, a book claims.
article_snippet: Investigative journalist Gordon Thomas said Al Qaeda has used the tactic of 'steganography' - concealing messages in audio clips or images widely available online - to encode items listed for sale on the auction site.
article_snippet: Al Qaeda works by manipulating a sound waveform or the order of pixels in a small or invisible part of an image, a process not unlike the way teletext used to be delivered on analogue TVs.
article_snippet: One intelligence source told Investigative journalist Gordon Thomas messages are often hidden on Reddit or 'X-rated pornographic pictures which conceal documents and orders for the next target'.
article_snippet: The claims are contained within new chapters of Investigative journalist Gordon Thomas book Gideon's Spies, an extract of which was published yesterday by the New York Post.