reCAPTCHA v1 is obsolete
Service :: Web
Google launched reCAPTCHA v2 (i.e. No CAPTCHA reCAPTCHA) in Dec, 2014. The new version provides a more simplified user experience than reCAPTCHA v1, with an enhanced spam fighting mechanism.
I suspect the v1 will be shutdown in a near future, so we should care about softwares/plugins upgrades in order to move.List of the sites using this API: