Steganography

Steganography is the science of hiding messages. Steganography is from the Greek for “covered writing”. The idea is that you can hide a file (or message) in an image. Images such as bitmaps and gif store the values for each pixel in a series of 3 bytes (where the first byte is for red, the second byte is for green, and the third byte is for blue). If you use the lower bit of the 3 bytes to store the bits of your hidden file, the image will still appear to be the same as the original image. An example of this can be found at http://www.cs.vu.nl/~ast/books/mos2/zebras.html (the web site for the book “Computer Networks” by Andrew S. Tanenbaum). In the Tanenbaum example he has a 1024X768 pixel bitmap that contains a compressed file of five complete works of William Shakespeare. (BTW “Computer Networks” is an excellent book and is the primary book that is used in the CSCIE-131b course that I am taking.)

This technique can also be used to watermark images and can also be used on music and video files (just imagine what you could store in a 1GB video file).

(There is no hidden file in this image)