Although we all should know basic maths, the math puzzle could cause some confusion. In your example i'm sure some people would answer with "8" instead of "1".

Would a simple string of text with random characters highlighted in bold or italics be suitable? The user just needs to enter the bold/italic letters as the captcha.

eg. ssdfatwerweajhcsadkoghvefdhrffghlfgdhowfgh

In this case "stack" would be the captcha. There are obviously numerous variations on this idea.

Edit: Example variations to address some of the potential problems identified with this idea:

• using randomly coloured letters instead of bold/italic.
• using every second red letter for the captcha (reduces the possibility of bots identifying differently formatted letters to guess the captcha)

Although we all should know basic maths, the math puzzle could cause some confusion. In your example I'm sure some people would answer with "8" instead of "1".

Would a simple string of text with random characters highlighted in bold or italics be suitable? The user just needs to enter the bold/italic letters as the CAPTCHA.

E.g. ssdfatwerweajhcsadkoghvefdhrffghlfgdhowfgh

In this case "stack" would be the CAPTCHA. There are obviously numerous variations on this idea.

Edit: Example variations to address some of the potential problems identified with this idea:

• using randomly coloured letters instead of bold/italic.
• using every second red letter for the CAPTCHA (reduces the possibility of bots identifying differently formatted letters to guess the CAPTCHA)

Although we all should know basic maths, the math puzzle could cause some confusion. In your example i'm sure some people would answer with "8" instead of "1".

Would a simple string of text with random characters highlighted in bold or italics be suitable? The user just needs to enter the bold/italic letters as the captcha.

eg. ssdfatwerweajhcsadkoghvefdhrffghlfgdhowfgh

In this case "stack" would be the captcha. There are obviously numerous variations on this idea.

Although we all should know basic maths, the math puzzle could cause some confusion. In your example i'm sure some people would answer with "8" instead of "1".

Would a simple string of text with random characters highlighted in bold or italics be suitable? The user just needs to enter the bold/italic letters as the captcha.

eg. ssdfatwerweajhcsadkoghvefdhrffghlfgdhowfgh

In this case "stack" would be the captcha. There are obviously numerous variations on this idea.

Edit: Example variations to address some of the potential problems identified with this idea:

• using randomly coloured letters instead of bold/italic.
• using every second red letter for the captcha (reduces the possibility of bots identifying differently formatted letters to guess the captcha)