How to add calculating captcha

the best captcha you can add is the calculation captcha which refreshes addition and simple calculation questions.

this captcha as in text even if directly copied from robots will give the error.

You can add them by adding a small php code.

Graphic or image captcha may also work but they are very hard for some users and you may lose the actual clients because of them.

search on google adding numeric captcha to website

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I found above article related to your topic and it has a video too.

post questions if you are not able to get it done