Understanding “Reverse CAPTCHAing”

I don’t know about you but to me I think the idea of CAPTCHA usage is a little backwards. We are asking humans to prove that they are human, how dumb. Plus not only that, but we are more then insisting that low/poor vision users don’t use our applications. Why not start thinking in reverse a little bit? Let’s make a form that makes the individual prove they aren’t a machine, not that they are a human.Confused? It’s simple – CAPTCHAs exist to prove that whomever or whatever is filling out the form is a human by reading some scrambled mess that a computer could not translate. However, machines behave logically – so we can easily test that a form is being filled out by something that is not a machine without making the user do something annoying like trying to recognize squiggly versions of alpha characters without having a brain aneurysm.

So how do we do this? Well simple… we add an input field to our form and then using a little CSS, hide it (style = “display:none;”). For the field label you could have “Please leave blank” – then for the input id = call it something typical, like city, name, email or whatever. But something that you aren’t using elsewhere on the form. So to review, you should have something like this:

<div style="display:none;">
  <label for="email_address">Please leave blank:</label>
  <input type="text" name="email_address" id="email_address" />

Now on the server processing page, check to see if this field is empty – if it isn’t, provide a friendly error that the form should be filled out manually.

So do you see how this works? Spiders and machines fill in fields they seen in a form – they add text to this field, and you simply ignore the interaction.

Before you complain about it, let me say it first. No. This technique is not applicable to all sites, such as news portals and such. But this will definitely help you reduce and spider related spam on those contact forms.