RE: Hidden digital signature in a graphic

["Steve Hudson" <steve -at- wright -dot- com -dot- au>]

I used the word 'chunk' hoping everyone would have had exposure to that word
in reference to data storage. To oversimplify, most file types have several
data 'chunks' in them. Each chunk has a different type of data. So a simple
graphics file format might use 4 chunks: one for the header with the file
type identifier, resolution and dimensions of the picture and one chunk each
for the red, green and blue picture components. Thus, using a hex editor or
several programming methods (even opening the file for append and writing
the info to it from VBA) can add 'isolated' data to the end of the file.

Some file types and filing systems require each chunk be properly identified
with a mini header providing the chunk data type giving the procedure
slightly more complexity. At the end of the day, this added text is tucked
in at the back of the file, where no self-respecting graphics program is
going to touch it, as it's not part of the picture data. The big
disadvantage therefore is the ability to seamlessly remove this information
without affecting the original image.


Steve Hudson , HDK List MVP
Wright Technologies Pty Ltd (Aus)





-----Original Message-----
From: Joyce Fetterman [mailto:JoyceF -at- gtsoftware -dot- com]

I'm confused by this. I don't understand what you mean about adding text
"after" the
bitmap. Can you explain a bit more please?

And does that mean you can search for the text to find whether anyone is
using your graphics on a Web site?


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