This version of the Independent JPEG Group's JPEG Software (release 4)
has been modifed for 1-bit steganography in JFIF output files.
Steganography is the science of hiding data in otherwise plain text or
images. Here, we are hiding the data inside images stored in the JFIF
format of the JPEG standard. It was believed that this type of
steganography was impossible, or at least infeasible, since the JPEG
standard uses lossy encoding to compress its data. Any hidden data
would be overwhelmed by the noise. The trick used by this
steganographic implementation is to recognize that JPEG encoding is
split into lossy and non-lossy stages. The lossy stages use a
discrete cosine transform and a quantization step to compress the
image data; the non-lossy stage then uses Huffmann coding to further
compress the image data. As such, we can insert the steganographic
data into the image data between those two steps and not risk
corruption.
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