If you have a magic band, it should automatically capture your ride photo on EVERY ride that offers pictures. Some people also choose to have their band scanned as a precaution about possibly missed photos or because they don't know that it's not necessary. Whenever I scanned my band at a photo preview station, I ended up with duplicates (presumably because the MB worked and I also scanned it again).
7 dwarfs is the one ride where you must have a MB or else there's no way to capture your photo (because there's no photo preview station at the end). There should be no rides where you must scan to get your picture. However, it's possible for photopass pictures to get lost and it's not a bad idea to check your account during your stay to make sure they showed up. If not, there's an online "report missing photos" button or a phone number to call and they're usually pretty good about finding your missing photos.