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You could use honey pot fields.

They provide a field within the form that is hidden from the user but designed to be noticed and filled in by any given bot.

They can be as simple as a field called 'phone_number' hidden with css. The bot doesn't process the css and sees the field, but the user doesn't.

This would work on both desktop and mobile and has been in circulation for quite a few years now.

Some more detail, including comments that cover accessibility concerns: http://haacked.com/archive/2007/09/11/honeypot-captcha.aspx/

Here Smashing Magazine outline this in more detail as well as dealing with some other Captcha methods:

http://coding.smashingmagazine.com/2011/03/04/in-search-of-the-perfect-captcha/

They also cite social login, image recognition and friend recognition as other more modern methodmethods, all of which could be implemented nicely on mobile, as well as showing in their poll that honeypots are the next most popular choice for their readers after traditional web form Captchas

PS a honey pot field is actually also a CAPTCHA, which stands for 'Completely Automated Public Turing test'. Learning about this principle may help with a general understanding of the underlying ideas.

http://en.wikipedia.org/wiki/CAPTCHA

You could use honey pot fields.

They provide a field within the form that is hidden from the user but designed to be noticed and filled in by any given bot.

They can be as simple as a field called 'phone_number' hidden with css. The bot doesn't process the css and sees the field, but the user doesn't.

This would work on both desktop and mobile and has been in circulation for quite a few years now.

Some more detail, including comments that cover accessibility concerns: http://haacked.com/archive/2007/09/11/honeypot-captcha.aspx/

Here Smashing Magazine outline this in more detail as well as dealing with some other Captcha methods:

http://coding.smashingmagazine.com/2011/03/04/in-search-of-the-perfect-captcha/

They also cite social login, image recognition and friend recognition as other more modern method, as well as showing in their poll that honeypots are the next most popular choice for their readers after traditional web form Captchas

PS a honey pot field is actually also a CAPTCHA, which stands for 'Completely Automated Public Turing test'. Learning about this principle may help with a general understanding of the underlying ideas.

http://en.wikipedia.org/wiki/CAPTCHA

You could use honey pot fields.

They provide a field within the form that is hidden from the user but designed to be noticed and filled in by any given bot.

They can be as simple as a field called 'phone_number' hidden with css. The bot doesn't process the css and sees the field, but the user doesn't.

This would work on both desktop and mobile and has been in circulation for quite a few years now.

Some more detail, including comments that cover accessibility concerns: http://haacked.com/archive/2007/09/11/honeypot-captcha.aspx/

Here Smashing Magazine outline this in more detail as well as dealing with some other Captcha methods:

http://coding.smashingmagazine.com/2011/03/04/in-search-of-the-perfect-captcha/

They also cite social login, image recognition and friend recognition as other more modern methods, all of which could be implemented nicely on mobile, as well as showing in their poll that honeypots are the next most popular choice for their readers after traditional web form Captchas

PS a honey pot field is actually also a CAPTCHA, which stands for 'Completely Automated Public Turing test'. Learning about this principle may help with a general understanding of the underlying ideas.

http://en.wikipedia.org/wiki/CAPTCHA

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source | link

You could use honey pot fields.

They provide a field within the form that is hidden from the user but designed to be noticed and filled in by any given bot.

They can be as simple as a field called 'phone_number' hidden with css. The bot doesn't process the css and sees the field, but the user doesn't.

This would work on both desktop and mobile and has been in circulation for quite a few years now.

Some more detail, including comments that cover accessibility concerns: http://haacked.com/archive/2007/09/11/honeypot-captcha.aspx/

Here Smashing Magazine outline this in more detail as well as dealing with some other Captcha methods:

http://coding.smashingmagazine.com/2011/03/04/in-search-of-the-perfect-captcha/

They also cite social login, image recognition and friend recognition as other more modern method, as well as showing in their poll that honeypots are the next most popular choice for their readers after traditional web form Captchas

PS a honey pot field is actually also a CAPTCHA, which stands for 'Completely Automated Public Turing test'. Learning about this principle may help with a general understanding of the underlying ideas.

http://en.wikipedia.org/wiki/CAPTCHA