2. Digital Image Steganography

         Digital image steganography is an information hiding system that strives for secure communication in a way that can go by completely undetected.  Steganograpy refers to the science of invisible communication, an acient art that travels as far back as to the Romans.  The Greek word translates to "covered writing".  Various methods allow these hidden messges to be sent through digital media.  Ivisible links, microdots, images, audio and character arrangement are among a few of these methods that makes it possible to conceal embedded data.  This system can be used for multiple purposes, ranging from good and bad intentions. 

          Steganographic software is a generally new invention.  There are two kinds of files typically used when embedding data.  A "container" will hide data in an ordinary-looking image.  A "message" is the information hidden in anything from plain text to other images, anything that can be embedded in the least significant bits (LSB) of an image.  A 24-bit image will use 3 bytes per pixel which can store information in the LSB of each byte allowing 3 bits to be stored in each pixel.   This allows the container image to appear exactly the same as the original picture when placed side by side.  Grey Scale images are a good candidate for encryption because the difference between the pixels are very subtle.  Images with drastic color changes draw more attention, defeating the purpose of being secretive.

http://www.jjtc.com/pub/tr_95_11_nfj/index.html
http://academic.research.microsoft.com/Publication/6454983/digital-image-steganography-survey-and-analysis-of-current-methods
http://fdyfiljasmine1.blogspot.com/2011/04/digital-image-steganography.html