After installing keycaptcha plugin please do the following:
- Login to your site as administrator.
- Go to System & Settings > Permissions & Access > Captcha setup.
- Activate keyCAPTCHA plugin. After that you should get userID and Private key from keycaptcha site.
- Register at https://keycaptcha.com;
- In your account click the link "Add site"
- Put all neccessary information about your site.
- At the last step you can see Private key. So, copy it to the Captcha setup page in your concrete5 dashboard.