internally signed JPEG files

[Sascha René Leib]

Hello all,

sorry if this has been discussed here already, I am new to this list, 
but before I spend my weekend coding I rather ask if somebody has 
already done this before.. :-)

I am planning to add a GPG/PGP signature to a JPEG file. However, the 
usual procedure of posting a hash key with the file does not appear 
very user-friendly to me, that's why I would rather like to go another 
way. In short:
  - create a signature for the JPEG-Data stream
  - insert this signature in a new marker segment in the JPEG file.

Since JPEG viewers should ignore unknown marker segments, this should 
not affect average end-users who can still view them conveniently in 
their web browsers, etc. For interested viewers, it should be easy to 
verify the origin and integrity of the file using a yet-to-write tool, 
or potentially even browser plugins.

Do you know if anyone has already taken some efforts into this 
direction, or do you know anything I ought to know?

Best greetings

/sascha

PS: of course, the same should also work with other "tagged" file 
formats, e.g. from the IFF-family (TIFF, ILBM, AIFF,...)