ScanGuard has a great space optimizer function.
ScanGuard will scan through your photos searching for any duplicates that you may not need anymore. It also scans through your apps and checks if there is any cached data that can be deleted.
Once the process has finished, it will take you to the summary page where you will be able to see how much space you can free up. The app will also show you how much of this potential free space is due to deleting duplicate pictures and how much is from clearing the cache.