1) The form encoding type needs to be set to multipart/form-data
in the DW tag selectcor, elect the form tag, then in the properties inspector, set the encoding type.
2) in the update behavior, you have bond the image fields to the file form elements.
on the bindings panel, there is a bindings group for the upload behavior. in the bindings group is a Server File Name binding you should use that binding instead of the file elements fro the form.