all you can really do is upload it, save it, and show it to them.
you could make your own tmp directory though
for example, user uploads, then you move from php's tmp dir to your special tmp dir
then show the user the image, linking to your special tmp dir
if they confirm it, then move from your tmp dir to to the final destination
you would want to use another script w/ cron to run once a day or whatever to go trhough your special tmp dir and delete everything though