My understanding is once you have selected a photo, they upload it in the background while you're doing other things (like typing the caption). If you decide to

My understanding is once you have selected a photo, they upload it in the background while you're doing other things (like typing the caption). If you decide to cancel it, I believe (hope) they delete it from the server. But it's the specific photo, not your whole album (that would be pointless ( and expensive) to do).