The filefield in PloneFormGen is a special case. The data submittee back to Plone is not included like other fields. I have little experience with the dtml you list, but you might get some inspiration from how PloneFormGen’s internal FormMailerAdaper is fetching the filefields in Python code and converting them to mime attachments. See the get_attachments method which is callled by send_form here:
The savedata adapter is not storing any filefields according to the documention. You field name of image_link is a bit confusing: are you storing a url to an image or using a filefield to upload a binary image?