v2 of the Google reCAPTCHA system.
https://developers.google.com/recaptcha/docs/display
Widgets
Get access to data on 2,906,083 websites that are reCAPTCHA v2 Customers. We know of 1,508,827 live websites using reCAPTCHA v2 and an additional 1,397,256 sites that used reCAPTCHA v2 historically and 850,649 websites in the United States.
Get a list of 2,906,083 websites using reCAPTCHA v2 which includes location information, hosting data, contact details, 1,508,827 currently live websites and an additional 1,442,407 domains that redirect to sites in this list. 1,397,256 sites that used this technology previously and 850,649 websites in the United States currently using reCAPTCHA v2.