I’m assuming this wouldn’t do well full scale as the spammers would catch on, but I recently saw a wordpress plugin which adds input fields to your comment forms that are hidden using CSS (e.g. display: none). Then if data is submitted in those inputs you can tell it wasn’t a human with a browser, but rather a spam bot filling all the fields as they usually do.

It’s a pretty simple concept to implement into a personal project or smaller site, and according to the plugin writer, completely eliminated all spam.

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