Yur screen shot shows a Binding group called Uploaded Files (upload) this binding group contains the server file name variable to use in the insert behavior.
see this tutorial for details on adding file upload to data Bridge insert and update pages:
http://www.webassist.com/tutorials/Add-file-fields-to-Data-Bridge-insert-update-pages
the security assist registration and user update pages are basically Data Bridge insert and update pages.