Design question - multiple form resubmit problem



My question has to do with a form resubmit problem. Say for example a
is submitted and within that form, a picture is uploaded. If the user
presses the Back buttom and gets back to the form submission sheet, and
clicks on resubmit, once again, the same data is populated into my
wasting space (another picture upload for no reason in a separate row).
Now, I know there are multiple ways of solving this issue, but where’s
best place to take care of this problem (e.g. just check in my action,
somewhere in the model?).



Well here’s what I would do, although I’ve never dealt with this
problem before so there could be far better ways, which I’m sure a
more experienced user will suggest. Don’t allow any one session to
upload a two images with the same filename and filesize.
Hope this helps.