Have a look at the first few bytes of some on-disk PIC files - there'll probably be an identifying string a few bytes long (e.g. MZ01PIC or the like).

Then scan the general field for this - that will provide the offset and also be a little more robust than the magic-number method.

If you are VERY lucky, the files will also have a trailing pattern (at the end of the file).

There are a number of web-sites that have the structure of files - I'm away from the office at the moment, but if you e-mail me I'll send you them on (my!) Monday.

(I've successfully used the above to extract Adobe Acrobat and Word files from Access 2.0 OLE files...just converting to VFP)