Steganography is the practice of concealing a message, file, or information within another message, file, or piece of information in such a way that it remains invisible to anyone who is not intended to see it.
The image depicted below, with dimensions 689 × 462, contains all 21,118 characters of the text “Dermatoglyphics,” hidden in the green color channel, which is undetectable by the naked eye.
First, the algorithm breaks down the Unicode characters of the plaintext into 16 bits. For example, the binary representation of D is 0000000001000100. It then stores each digit in the least significant bit of the green color value, using 16 adjoining pixels per Unicode character.
Given that an uncompressed image file format (such as Bitmap or TIFF) is maintained, the information can easily be extracted by the intended recipient of the message with a reverse algorithm. However, the use of uncompressed images might be seen as a disadvantage, as they stand out in modern web culture with highly efficient image formats (such as WEBP).
Of course, the image size could be further reduced if more than the least significant bits were used for data storage. However, it is important to keep in mind that altering more bits will make it more apparent that the original image was modified. Alternatively, the red and blue color channels can also be utilized to achieve even smaller images. Moreover, the encoding could be changed to use 8 bits instead of 16 bits, losing only a few special characters in translation but further decreasing the image size by half.
On a side note, it should be mentioned that Stegano Green is less secure when used with computer graphics as opposed to photos. Because computer graphics tend to contain large areas of equal color values, the altered least significant bits become more obvious.
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