| Challenge | Explanation | |-----------|-------------| | | After ~30 page downloads, Google presents a reCAPTCHA. | | Rate limiting | IP-based blocking after 50-100 tile requests. | | Dynamic tile URLs | Google now uses short-lived signed URLs with &sig=... that change per session. | | Missing pages | Preview mode often skips 10-20% of pages (e.g., every 10th page omitted). | | Low resolution | Max zoom = 2 gives ~150 DPI, unreadable for technical books. |