Well, you wouldn't want to rely on iCloud backup for all of your photos anyway. You should be importing your photos regularly to archive them. You can import them to a photos app on your computer (iPhoto or Photos on a Mac, or the photos app on a Windows machine), or upload them to a cloud service like Dropbox.
If you have a Mac and you are running the latest OS X on it, you can use iCloud Photo Library as a repository, however, iCloud Photo library also changes the way that photos are shared and displayed on your iOS devices, so you would want to read up on it before moving to that process.
But a simple and regular import to your computer is the easiest way to ensure that your photos are archived in a safe place:
PHOTO IMPORT IOS TO MAC/PC
Best of luck,
GB