Media upload and abuse screening

Design the upload + validation pipeline for a public user-generated image/video host (think Imgur) accepting anonymous and authenticated uploads at 20K uploads/sec. Uploads must be validated (real media of the claimed type, within size limits), screened for abuse (CSAM/NSFW/malware), and made available quickly, but a malicious user must not be able to exhaust storage, smuggle a non-media payload, or get illegal content served even for a moment. Design the ingest path, validation ordering, and abuse defenses.