Topic Author
Posts: 535
Joined: Mon Mar 12, 2001 4:19 am

Invisible Watermark? Where And What?

Fri Jul 06, 2001 5:39 am

The photo usage page of this site says all pictures carry an invisible watermark. Where is it and what is it? How can you see it?
Bring it back, bring it back, bring it back
Posts: 2888
Joined: Wed Nov 01, 2000 12:52 am

RE: Invisible Watermark? Where And What?

Fri Jul 06, 2001 5:44 am

If it's invisible, I don't think you can see it  Smile

Seriously, I'd be curious to know myself.....


RE: Invisible Watermark? Where And What?

Fri Jul 06, 2001 8:01 am

Hey ,
I could be way off here, in fact I probably am, but as far as I know there is a way of embedding text in the .jpg file.

Perhaps this is how it is done, maybe not, but it's something to think about!

It was used in the movie 'Along Came A Spider'
The rich kids in the movie used this method to pass notes around the class,
no-one knew what they were doing, cause it seemed as if they were just sharing pictures.

Don't blame me if I'm totally wrong!!

Posts: 9973
Joined: Mon Apr 23, 2001 10:12 pm

RE: Invisible Watermark? Where And What?

Mon Jul 09, 2001 3:57 am

There is a way to add extra headers to a JPEG file that can contain just about anything. A good program that does not recognise these headers should leave them in place (a bad program may remove them...).

From a document on the JPG format:
"APP0 marker used for application-specific information

Additional APP0 marker segments can be used to hold application-specific information
which does not affect the decodability or displayability of the JFIF file. Application-
specific APP0 marker segments must appear after the JFIF APP0 and any JFXX APP0
segments. Decoders should skip any unrecognized application-specific APP0 segments.

Application-specific APP0 marker segments are identified by a zero terminated string
which identifies the application (not "JFIF" or "JFXX"). This string should be an
organization name or company trademark. Generic strings such as dog, cat, tree, etc.
should not be used. "
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