[eluser]mddd[/eluser]
I agree with adamp1, save the file somewhere so you can keep track of it. Finalize it when done. Prevent the user from having to upload twice.
One thing to look out for: you need to remove the file when it ends up not being used. For instance if the user decides not to continue with the process of adding.
This could be as simple as checking if there are no files older than a day in the upload folder, and deleting them if there are any.
Another thing: it is not always necessary or even useful to have the pictures named by the id of the item. What if you want to upload more than 1 file per item? I usually name the picture uniquely by getting a uniqid() and then store the id with the item. This also solves the problem of not knowing the item's id. You don't need to know it for storing the picture.