Steganography is the method for hiding secret messages in other messages, such that the secret’s very existence is concealed. Generally the sender writes an message and then conceals a secret message on the same piece of paper. Throughout history tricks have been made use using invisible inks, tiny pin punctures on selected characters, minute differences between handwritten characters, pencil marks on typewritten characters.....and of course IMAGES[remember DA VINCI? and the debut MONALISA SMILE]
Steganography is the art or practice of concealing a message, image, or file within another message, image, or file.[Its based on your incapability of persiving small changes,So beware---This speaks "What you see is Not what you Believe"]
But we are going to discuss about the art of hiding message in an Graphic image[LOL,this is the age of computers not the 14 the century Canvass painting]
This is done by replacing the least significant bit of each byte of the image with the bits of the message.This wouldn't change the graphic image appreciably as most graphics standards specify more gradations of color than the human eye can notice......and the message can be stripped out at the receiving end.
You can store a 64-kilobyte message in a 1024 × 1024 grey-scale picture this way
[OVERVIEW OF THE GRAPHICS BACKGROUND]
A pixel is a single point in a graphic image. Graphics monitors display pictures by dividing the display screen into thousands (or millions) of pixels, arranged in rows and columns. The pixels are so close together that they appear connected.
The number of bits used to represent each pixel determines how many colors or shades of gray can be displayed. For example, in 8-bit color mode, the color monitor uses 8 bits for each pixel, making it possible to display 2 to the 8th power (256) different colors or shades of gray.[[[For simple monochrome images, one bit is sufficient to represent each dot, but for colors and shades of gray, each dot requires more than one bit of data.]]]
The density of the dots, known as the resolution, determines how sharply the image is represented. This is often expressed in dots per inch (dpi) or simply by the number of rows and columns, such as 640 by 480.
The encryption of a plain text message is done by selecting the last bit, in a 8 bit pixel word, and replaces it with a single bit from the cipher text. That change is so insignificant that it does not alter the appearance of the image as viewed on a computer display.
Now lets get practical,we will hide the character 'S' is an eight (8) bit byte which is represented in binary form as 01010011.
The series of nine pixels from the image, three pixels each made up of three pixels RGB(red, blue and green) are used for the needed eight bits, with one left over to be used for the first bit in the next character of the message.