Looks fantastic! As someone who has done it before, if this gets popular you'll run into some abusive users that you'll want to deal with. Microsoft will often give out free access to it's PhotoDNA service for detection of explicit images of minors. VirusTotal will often do the same for malware in exchange for samples. You'll also want to have a structured retention process, e.g. size is inversely proportional to storage time.
Good luck, get in contact (see my profile) if you run into any issues.
Good luck, get in contact (see my profile) if you run into any issues.