I had my iPhone replaced, and restored my data from the iTunes backup. Unfortunately, now iPhoto thinks the photos that were restored from backup are new photos, and so it does not hide them when I choose "hide already imported" in the import screen. Is there a way to get it to recognize that these photos are already in the library? I'm using iPhoto '09.
Unfortunately, the only way seems to be to import the duplicates and keep them, while manually deleting the original copy (i.e. the one imported from the old iPhone).
I'm assuming that the photos you're talking about are on the Camera Roll on the iPhone? You could let iPhoto go ahead with the import anyway and when it recognizes duplicate photos it will prompt you if you want to re-import them or not. Just choose No at that point. I'm not 100% sure, but I believe that after that it will regard the photos on your iPhone to have been imported and not show them any more if you have "Hide already imported" selected.