are you talking about a DataAssist insert and Update pages?
if so, there is a fix for this issue in the known issues section of the DataAssist download center page.
to upload images when inserting a product using data assist, you will nee to use the File Manipulations -> Upload Files functions included with either Universal Email or CSS Form Builder. There used to be a standalone product named Digital File Pro that is now bundled into those 2 extesnions.
on the DataAssist support page, there is a tutorial titled:
How to apply Digital File Pro to DataAssist Insert and Update pages
that will help you with using file upload in data assist page: