@BasePlay
It doesn't mean they check the site manually. The bot probably scrapes multiple sites and checks file size. Extreme discrepancies probably get rejected automatically while multiple will flag manual review.
It also wouldn't be unusual for scrapers to require manual reviewing before upload.
Your best bet are watermarks and randomizing link url's (not having site.com/manganame/chapter1) with links to next chapter redirecting you to a non-standard bot checker.
You can make failed checks link back to random chapter to make it look legit to random people reviewing