You could access photo stream photos from the last 30 days by signing into your iCloud account on your computer and enabling photo stream. This article explains how to set up iCloud on your computer: http://www.apple.com/icloud/setup/.
However, the only way to access camera roll photos contained in your iCloud backup is to restore the backup to another iPhone. If you don't have one, perhaps you can ask a friend who does to help you. They would need to back up their phone to their computer using iTunes, then restore your iCloud backup and import the recovered photos to their computer, then restore their iTunes backup to return their original data.