CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) is a challenge mechanism designed to block automated requests. Common forms: image recognition puzzles, audio challenges, invisible behavioral analysis (reCAPTCHA v3), and proof-of-work challenges like Cloudflare's Turnstile.
CAPTCHAs are the primary defense layer for high-value scraping targets. Solving them programmatically requires either human-labor CAPTCHA farms, AI-based solver APIs (2captcha, Anti-Captcha, CapSolver), or browser fingerprint quality good enough to pass behavior-based challenges without triggering them. CAPTCHA solving adds latency and cost to any scraping pipeline that encounters it.