This is an ongoing problem that needs to be addressed in ASP as well as PHP.
The documentation will work just fine if your form has nothing but a file field on it or if you never wish to replace the file but the logic fails when you want to have full control of the file and record.
Setting Default File Name will address the issue of updating the record without uploading a new image but it forces you to retain the original file name and that is not always desireable.
If the original filename is acceptable to you it will still conflict with a file delete behaviour.
The trigger to delete the original file is "Upload Successful". If I successfully upload an image, rename it to the original file name and update the database the very next step will delete the very file that I just uploaded.
DFP on a DataAssist needs better logic built into it.
If I update a record, without uploading a new image, the imagename field needs to be left intact.
If I upload a new image, the imagename field needs to be set to the ACTUAL new name of the image.
On succcessful Upload I can then delete the original filename.
Some sort of IF THEN ELSE logic should do it but I cannot write it.