By downloading the Google+ App, you can have Google automatically back up your photos. Even better, you can set it up so that backup only happen when your connected to a WiFi network. (No burning valuable cellular minutes.) All backup photos and videos are kept in private area of Google+.
Photos that are at least 2048px are backup for free on Google+. The iPhone uses 3264 x 2448 for photos. If you choose to have the full version backed up, just make sure you manage your account frequently. Google gives you 15GB for free, which means that you would only be able to store approx 7,500 photos. The 15GB is shared with other Google Apps such as Mail. Taking movies, that uses up more of your Google+ space.
I know that 7,500 photos sound like a lot, but remember if you don't manage your photos, the storage space can add up very quickly.
This is very handy App to have when traveling to Disney World. Take all the photos you want during the day. When you get back to the hotel room, you can backup your photos when you connect to the free hotel wifi. When it's all done you can go through the photos camera roll and delete unwanted photos or videos. Do you really need to keep 200 photos of the parade?
If you only plan on using the photos online, don't bother using the full size backup. You wouldn't notice the difference of quality, and you don't have to worry about how many photos you have on Google+. Basically you'll be able to take a years worth of photos without paying Google anything.