In the Insert record server behavior, you are binding the Image columns to the file Form elements.
Digital File Pro Creates a new data binding group WA Uploaded Files (File Field Name)
In this group is a Server File Name variable. One is created for each upload location, for example:
images/thumbs/[FileName]: Server File Name
images/imagesmedium/[FileName]: Server File Name
In the insert record server behavior, you should bind the image columns to the Server File Name Varibles created by DFP.
See the How to apply Digital File Pro to DataAssist Insert and Update pages tutorial on the DataAssist support page in the How To section: