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Fighting spammers is one of the tougher jobs of a website owner or administrator. One tool we provide, and that you should use if not using reCaptcha, is the Anti-Spam Questions with Images. You can google around for tips on making some but many site owners use their niche for ideas for the questions. This tutorial will show you how to enable and add anti-spam questions.
If you need to edit your anti-spam question(s), just click the small drop-down menu on the left of the image you want to edit, you will see the question and things you can change. Be sure to click Edit Question when done editing it as that will save the edits.