From theregister.com
Analysis Six years ago, Google revised its reCAPTCHA service, designed to filter out bots, scrapers, and other automated web browsing, and allow humans through to websites.
The v2 update in 2014 added an iframe or HTML Inline Frame, which is a way of embedding one web page in another. Then there was the v3 update in 2018, which added machine learning to the mix, to reduce the need for interaction with bot detection challenges.