RE: Hiding Data in jpg or bmp files

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Catch me if I am wrong, since i am no expert in the area of images.
Each pixel in a BMP with 16M colors is made up of 3 bytes, one each for Red,
Green and Blue. This gives a color depth of 255 for each of those colors.
It would be quite easy to make a program that alters the least significant
bit for each (or some) of those bytes to hide a hidden message and this would
alter that bits intensity of its color only by a 1 to 255 ratio. So it would
be next to impossible to spot any faults in the tampered with BMP, even if u
the original and could compare them side by side. Remember it would be random
if the bit was set to zero or one (half the bits wouldnt be changed), so the
overall light intensity of the pic would be the same.
So in a small BMP (say 100x100) u have 30k bytes, divede that by 8, and u
could hide almost 4k characters if u used all bytes. The program should
cryptate the msg. before inserting it, so all u would have to make sure of
was that the recieving end had your program and PW to read and decrypt the
msg.

"Kahuna" wrote:

> Hi Folks
>
> I have heard of data being hidden in Bitmap or JPEG Files, usually related
> to security information. Does anyone have links to resources where I can
> find out more on how this is done?
>
> I can read the headers on bmp's and read the file into a form etc, but I
> dont understand how a security data string could be encoded into the file
> without detriment to the image.
>
> Any info appreciated
>
> --
> Kahuna
> ------------
>
>
>
.

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