POST /api/x402 with {"action":"art_judge","image_url":"https://..."} to receive a 402 with payment requirements. Sign the payment in USDC on Base, resubmit with the x-payment header, and get back a job_id. Poll /api/x402/status/{job_id} every 5–10s until completed — result includes a score (0–10) and written critique. Batch up to 5 images at once with art_judge_batch. $0.2020 USDC per image, no API key required.