ABSTRACT
As outlined earlier, information can be hidden in various
formats, including text, images, and sound files. In this
entry, we limit our discussion to hidden information in
graphic images. To better understand how information can
be stored in images, we need to do a quick review of the
image file format. A computer image is an array of points
called pixels (which are represented as light intensity).
Digital images are stored in either 24-or 8-bit pixel files.
In a 24-bit image, there is more room to hide information,
but these files are usually very large in size and not the ideal
choice for posting them on Web sites or transmitting over
the Internet. For example, a 24-bit image that is 1024 768 in size would have a size of about 2 MB. A possible solution
to the large file size is image compression. The two forms of
image compression to be discussed are lossy and lossless
compression. Each one of these methods has a different
effect on the hidden information contained within the host
file. Lossy compression provides high compression rates,
but at the expense of data image integrity loss. This means
the image might lose some of its image quality. An example
of a lossy compression format is JPEG (Joint Photographic
Experts Group). Lossless, as the name implies, does not lose
image integrity, and is the favored compression used for
steganography. GIF and BMP files are examples of lossless
compression formats.
