Try this hack from Donna Baker. It only inserts PDFs but users can easily convert images such as JPGs to PDFs. This suggestion should be on the Acrobat forum I suppose, but I think many InDesign form creators will be interested. Let's hope a future version of Acrobat will allow us to do this properly.
I believe this feature can be implemented in LifeCycle but that's not for normal mortals!
Derek
