Alternatives to image captcha's?

[Tandem]

Just out of interest, I was wondering if anyone knows of any alternatives to the image using captcha's?

I have a form on my website, where the more a person submits a form the more credits they get for there account. They can only submit it every 2 minutes, but i had to introduce a captcha to stop people scripting and auto-reloading.

I was thinking of a system where every 5-10 minutes, instead of the form, a checkbox appears, and they have to check it and submit that before they can do the form, but if any of the post data is being sent when it isn't needed, such as would be done by an auto-reload, then the form doesn't process. But a could scripter could get around it quite easily however.

Anyway, yeah. As the first question says, anyone know any alternatives to captchas that display an image that you have to write into the box etc?

[bibby]

My friend is using picture trivia, using random photos found on the net. There are a series of questions possible questions associated with each photo, so the photo can be reused. This of course is not a very good use of his time (creating questions and answers), when it should be random.

For example, a photo of hot babes at a bar. Questions would be, "What color is the redhead's shirt?", "How many bottles are on the bar?".


What's the problem with captchas anyhow?

[Tandem]

From my point of view, nothing. They're effective at what they do, they're just immensely unpopular with users, and there doesn't seem to be any alternative.

[Jessica]

There are several nice alternatives. Check the content for text you don't want, and only make them enter a captcha if it contains that text. (such as viagra, etc.)

Use a math captcha (two plus two equals? and user types in four.)

[redarrow]

I like the idear i had years ago use a pic of a animal then tell the user to press that animal.