I assume I would have to open the file as a BINARY type.
Any idea where I can find some detail about the format ?
The stuff I want to do is not included in their typical software for opening the file directly.
JPEG files are binary files with a compression scheme. There are probably a lot of libraries out there that you can use to manipulate them. ImageMagick is certainly a good candidate (http://www.imagemagick.org/script/index.php). I do not know of Fortran bindings, but they should not be too hard to write.
Wikipedia has a long page on the subject: https://en.wikipedia.org/wiki/JPEG
Depending on the amount of effort you want to put in, interfacing to an existing library may or may not be an attractive solution.
OK, thanks for your responses !
I will take a look at the stuff -
What I need to do is not normally supported, since it involves some encryption.
I basically need to get the "raw" pixel format, so I can load it into a Fortran program.