Re: Stego - images and sounds

["E. ALLEN SMITH" <EALLENSMITH@mbcl.rutgers.edu>]

From:	IN%"sasha1@netcom.com"  "Alexander 'Sasha' Chislenko"  9-MAR-1996 22:59:54.01

>At 12:19 PM 3/8/96 -0800, Jim McCoy <mccoy@communities.com> wrote:
>>
>>Provided the bits are random in the way that they should be... The low-order
>>bits in such files were chosen by implementors of stego programs because
>>modification would not be noticed by the person viewing or listening to
>>the file, not necessarily because there was actually randomness at this
>>level which could be replaced.  Does anyone know of a survey of images or
>>sound files which tested the statistical randomness of these bits?  They
>>may not be as random as people think they are.
>>

> This should depend on how the image/sound was obtained, though I am pretty
>sure in most cases there would be easily detectable patterns.  They would
>be the strongest in software-generated files, smaller in good reproductions
>of precise recordings, and very small in noisy recordings.  In all cases,
>the number of lower bits used for stego-messages may be chosen lower than
>the existing noise of the signal.  Changing all lower bits in a good
>rendered image may still be unnoticeable for the human viewer, but really
>easy to detect to a program.

	Unless the picture, sound, whatever has a periodic function, the LSB
ought to have an approximately random distribution (barring all 0's and all
1's, for full color saturation). The periodic function part could be a problem.
	-Allen