Proof of Work Captcha We offer an easy to implement captcha-like service where users need to solve a number of hashes (adjustable by you) in order to submit a form. This prevents spam at an inconvenience that is comparable to a classic captcha. All with the added benefit of earning you money. An alternative for Google's reCaptcha For an example, have a look at our signup page. The captcha API is modeled after Google's reCaptcha. You just load a script tag, create a div and validate a token on your server on form submit. See the detailed implementation guide in the documentation.