easier it is to hide a "needle"). So digital pictures, which contain much data, are sometimes used to hide messages on the Internet and on other digital communication media. It is not clear how common this practice actually is. For example, a 24-bit bitmap uses 8 bits to represent each of the three color values (red, green, and blue) of each pixel. The blue alone has 28 different levels of blue intensity. The difference between 11111111 and 11111110 in the value for blue intensity is likely to be undetectable by the human eye. Therefore, the least significant bit can be used more or less undetectably for something else other than color information. If that is repeated for the green and the red elements of each pixel as well, it is possible to encode one letter of ASCII text for every three pixels. Stated somewhat more formally, the objective for making steganographic encoding difficult to detect is to ensure that the changes to the carrier (the original signal) because of the injection of the payload (the signal to covertly embed) are visually (and ideally, statistically) negligible. The changes are indistinguishable from the noise floor of the carrier. All media can be a carrier, but media with a large amount of redundant or compressible information is better suited. From an information theoretical point of view, that means that the channel must have more capacity than the "surface" signal requires. There must be redundancy. For a digital image, it may be noise from the imaging element; for digital audio, it may be noise from recording techniques or amplification equipment. In general, electronics that digitize an analog signal suffer from several noise sources, such as thermal noise, flicker noise, and shot noise. The noise provides enough variation in the captured digital information that it can be exploited as a noise cover for hidden data. In addition, lossy compression schemes (such as JPEG) always introduce some error to the decompressed data, and it is possible to exploit that for steganographic use, as well. Although steganography and digital watermarking seem similar, they are not. In steganography, the hidden message should remain intact until it reaches its destination. Steganography can be used for digital watermarking in which a message (being simply an identifier) is hidden in an image so that its source can be tracked or verified (for example, Coded Anti-Piracy) or even just to identify an