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!
InDesign does not have support for an "Image Field" as part of it's Buttons and Forms functionality. You also can't associate an 'attach' or 'insert' image action to a button control. You could use Adobe LiveCycle Designer to add this functionality.
- You can start your form design in InDesign and could add some basic form elements such as text fields and save this file as an Interactive PDF.
- In LiveCycle Designer, when you open the interactive PDF you've created in InDesign, the PDF will undergo some changes and you might find that things like buttons don't quite work or change in appearance - which is why I'd suggest you verify all of your form elements still work when previewing the PDF form in LiveCycle Designer and update/fix the ones that don't
- In LiveCycle Designer, you have a field type called "Image Field' (Object Library panel). When such a field is clicked in the PDF, the user is prompted to navigate to an image on their system (JPEG, PNG, GIF and TIFF are supported file formats), and insert it in the Image Field area.
If you are looking at doing and need more support please ask any follow-up questions in the LiveCycle Designer Community.