To clear images and zip archives cache run first command. Old files will be deleted if hole size will be bigger than gallery available. To remove users cache directories run second.
python manage.py clearcache python manage.py clearcache full
By default this command run every hour.
To detect images that not available on storage run checkimages command. It iterate all holders images and check that path exists. After send report to email if not found at least one.
python manage.py checkimages
By default that command run at 00:00 every day.