Since you do have 29 GB of photos, if you only have the 5 GB you get for free in iCloud, that could be why your backups are so large. If this is the case, then not all of your photos are in iCloud, and they will be included in iTunes backups. Unfortunately, iTunes does not let you choose what to include in backups. It's either everything or nothing and you don't have control over this.
Another thing to try is to make sure that you only have the backups you need. While in iTunes, in the menu bar, click on 'iTunes' and go to Preferences. In the window that comes up, go to the 'Devices' tab. In here, you should see your device backups and their dates. There should only be one backup per device you have synced with iTunes. If for some reason you have multiple, you can delete the oldest ones. If you have backups for devices you don't use anymore, feel free to delete those as well.