As the general field contains OLE data, the retrieval of the file from it was created is not a simple task, and in my humble opinion is Application/Windows-Class dependant. In other words - nearly impossible if you do not have control on your application environment

If on my computer:
the .jpg file says in registry that it is jpegfile,
the jpegfile says that its CLSID is {11943940-36DE-11CF-953E-00C0A84029E9}
and that CLSID has a description of "Microsoft Photo Editor 3.0 Photo"

...on other computer the situation may be different.

Note that when you bound an OLEBoundControl to General field, you can edit the data in this field, with the program, the contents of General field is associated

btw. I am curious about how you did it for a BMP image?
using API functions?
(I have not encountered such a problem, but it is interesting to me... but not so much, to force my company to pay for it:)