 BetterPhoto Member |
Hiding information using threshold control. I am analyzing a set of documents which on the surface appear to be nothing more than photos of commercial greeting cards. If these documents are viewed in Photoshop using the threshold function, stepping through the threshold levels from 0 to 255 generates a series of distinct images which are not visible otherwise. This is not a random phenomena. Someone purposefully modified the documents using some type of photographic or lithographic process to hide these images as a kind of steganographic technique. When stepping through the threshold values from 0 to 255 or in reverse, images appear and then disappear in the fashion of a crude animation. These documents were produced in the late 60's and early 70's. My question is: By what photographic process could the originator of these documents insert these images so that they can only be seen by changing the threshold values as I decribed?
|
|
|
|
||
|
Christopher A. Vedros |
I'm not an expert in steganography, but it seems to me if there are images hidden in these documents, they were inserted into the electronic scans, and not in the original photos. Just my guess.
|
|
|
|
||
|
This old forum is now archived. Use improved Forum here
Report this Thread |
||