Jani - Different kinds of CAPTCHA

Different kinds of CAPTCHA

Thursday, April 26, 2007 6:27:17 PM

Most of us have probably seen a CAPTCHA image: A image with some fuzzy lines, noise and stuff and a bunch of letters that we are supposed to type into a box to verify that we are indeed human and not a computer.

There are other types of tests to determine whether one is a human or not, some even better than the images... but for some reason they aren't used as widely as images.

Let's look at some different methods to determine the users' humanity

The simplest version of a different test is just to have a textbox and a static message such as "type foobar to the box". Most spambots can't figure out even such simple things.
Other versions of this include simple math problems such as 2+2=? or an item the user must choose from a dropdown list.

Other quite simple methods include checking if two values in your form contain the same values: For example, if you have a first name field and a last name field, it's highly unlikely that they both should contain the same value. Is there anyone called Peter Peter? Don't think so.
Another approach is to check for HTML input in fields which shouldn't require any.

A bit more complicated approach is to create a fake name field. Most spambots will try to fill in fields that have the name attribute set to things such as "name" or "firstname"... So in addition to the actual fields, add a field with a name like that and hide it with CSS. Because bots can't parse CSS they will see the field and fill it... so you simply check if the field is filled and from that you can know it's a bot. Some precautions are in order, though: Text-only browsers might ignore the CSS to hide the field and thus you should add some text to accompany the field that tells to leave it empty.

You can also check the browser headers. 99% of real browsers fill in Accept Language and Accept headers... so if they are empty, you have a bot.

The methods mentioned above are as foolproof as using scrambled images. Also, a user with disabilities might not be able to see the fuzzy image at all, so there's also the usability issues of using images to detect bots. In a high-traffic site, generating images may also take considerable amounts of processing power.

So why aren't different methods used instead of images?

What kind of a coder are you?Opera goodies

Comments

Anonymous # Monday, November 5, 2007 8:23:08 PM

stephe writes: Why not switch to those tasks which humans find easy but computers find hard? If everybody used "2+2=" it wouldn't take the botwrights long to figure out ways of answering this, and the current craze for letters+digits+noise can produce images that even humans find hard to decypher, but we can recognise famous faces (even allowing for cultural differences, there are some people who should be recognisable to pretty much all the online population), distinguish between cats and dogs, call a spade a spade, etc. Sites need not use precious processing power to generate these images, just choose them from a pool, and they can be large and clear enough for anybody able to see the screen. PS: I keep getting a security code error with this!

Janizomg # Tuesday, November 6, 2007 4:46:14 AM

I wouldn't use images of famous people, but perhaps a choice of three common items would be a good idea. Maybe show an image of a dog, a cat and a bird and then tell the user that they need to click the dog... what they need to click would be randomized every time of course.

Anonymous # Wednesday, August 27, 2008 11:01:26 PM

Anonymous writes: THH

Anonymous # Friday, October 15, 2010 8:02:41 PM

Анонімний writes: Every one remembers that modern life is expensive, but different people require money for various things and not every one gets big sums cash. So to receive fast business loans or just secured loan would be a proper solution.

Anonymous # Sunday, January 16, 2011 6:20:16 PM

Анонімний writes: I think that to get the business loans from creditors you must have a great motivation. Nevertheless, once I have received a commercial loan, just because I was willing to buy a bike.

Anonymous # Tuesday, January 25, 2011 7:01:46 AM

Anonymous writes: ertyergwerfgwerftg

Anonymous # Tuesday, March 29, 2011 3:10:08 PM

Анонімний writes: Cars and houses are not very cheap and not everybody can buy it. But, loan was created to aid different people in such kind of cases.

Anonymous # Tuesday, March 29, 2011 3:10:38 PM

Анонімний writes: Buildings are not cheap and not everyone is able to buy it. However, home loans are created to aid different people in such kind of cases.

Anonymous # Tuesday, March 29, 2011 3:11:06 PM

Анонімний writes: I would like to propose not to hold back until you earn big sum of money to order all you need! You should get the loans or car loan and feel fine

Anonymous # Tuesday, March 29, 2011 3:11:30 PM

Анонімний writes: I would like to propose not to hold off until you earn big sum of money to order different goods! You should just take the mortgage loans or short term loan and feel fine

Anonymous # Tuesday, March 29, 2011 3:12:04 PM

Анонімний writes: Do you recognize that it's the best time to get the mortgage loans, which can make you dreams real.

Anonymous # Tuesday, March 29, 2011 3:12:32 PM

Анонімний writes: Houses and cars are not very cheap and not everybody is able to buy it. But, home loans was created to help people in such cases.

Anonymous # Tuesday, March 29, 2011 3:13:15 PM

Анонімний writes: The loan are useful for guys, which want to organize their career. By the way, it is very easy to get a car loan.

Anonymous # Tuesday, March 29, 2011 3:13:46 PM

Анонімний writes: It's known that cash makes us disembarrass. But how to act if somebody does not have cash? The one way is to receive the business loans and just short term loan.

Anonymous # Tuesday, March 29, 2011 3:14:25 PM

Анонімний writes: Following my exploration, millions of people in the world receive the credit loans from well known banks. Therefore, there is great possibilities to find a auto loan in all countries.

Anonymous # Tuesday, March 29, 2011 3:14:59 PM

Анонімний writes: People all over the world take the personal loans in different creditors, because this is simple.

Anonymous # Tuesday, March 29, 2011 3:15:38 PM

Анонімний writes: When you are in not good state and have no money to get out from that point, you will require to take the mortgage loans. Just because it would aid you unquestionably. I get short term loan every time I need and feel myself fine just because of this.

Anonymous # Tuesday, March 29, 2011 3:16:22 PM

Анонімний writes: Following my own analysis, thousands of people in the world receive the personal loans at different banks. Hence, there is good possibilities to get a college loan in every country.

Anonymous # Tuesday, March 29, 2011 3:16:38 PM

Анонімний writes: Do you understand that it's correct time to receive the home loans, which would make you dreams real.

Anonymous # Tuesday, March 29, 2011 3:17:26 PM

Анонімний writes: Set your own life time more easy get the personal loans and all you want.

Anonymous # Tuesday, March 29, 2011 3:18:04 PM

Анонімний writes: Make your life time easier take the home loans and all you want.

Anonymous # Tuesday, March 29, 2011 3:18:29 PM

Анонімний writes: I think that to get the loans from creditors you ought to have a firm motivation. Nevertheless, one time I've got a car loan, just because I was willing to buy a building.

Anonymous # Tuesday, March 29, 2011 3:19:03 PM

Анонімний writes: Houses are not very cheap and not everybody is able to buy it. Nevertheless, home loans are created to help different people in such kind of hard situations.

Anonymous # Tuesday, March 29, 2011 3:19:23 PM

Анонімний writes: Cars and houses are quite expensive and not every person is able to buy it. However, credit loans are invented to aid different people in such hard situations.

Anonymous # Tuesday, March 29, 2011 3:19:41 PM

Анонімний writes: I would like to propose not to hold off until you get big sum of money to buy all you need! You should just take the credit loans or credit loan and feel comfortable

Anonymous # Tuesday, March 29, 2011 3:20:05 PM

Анонімний writes: It is good that we are able to receive the loan and it opens new opportunities.

Anonymous # Saturday, July 16, 2011 10:17:38 AM

Anonymous writes: dgfdhghgfjhgjh

Anonymous # Tuesday, September 27, 2011 12:17:17 PM

Anonymous writes: Captcha is getting post with invalid entered captcha value.

Write a comment

Blog search

Me

CodeUtopia blog

Zend Framework components as separate zips fro ...
Did you ever want to use just a single component from Zend Framework, but couldn’t figure out which files you needed? Well, here’s a solution: Zend Framework packageizer script! Just pick the class you want, and you’ll get it and all its dependencies in a nice zip file for you ...
Making a PDF generator class using Zend_Pdf
There are some expensive libraries that you can use to generate PDF files… but why bother with them, when there are good free alternatives like Zend_Pdf? In three steps, you can generate a fancy report: Create a PDF template Insert data to template with Zend_Pdf Profit $$$ Since this is ...
Let’s Rickroll MTV Europe Music Awards 2008!
Okay so this is totally off the usual topics I guess, but this is too awesome to let it fail! Rick Astley has somehow managed to get into MTV Europe’s Music Awards 2008 gala in the category Best Act Ever. I suspect /b/ had something to do with this, but… I urge everyone to vote for R ...
Windows Remote Desktop + Live FolderShare = Ul ...
I’m a frequent user of Windows’ remote desktop feature. It’s a stellar remote control solution: It’s incredibly fast, almost like sitting on the remote PC, and has features like bringing over the clipboard and even sounds from the controlled computer. Much better than VNC ...
Sharing authentication over multiple sites / S ...
At The Group, we’re developing some web applications that needed to use the same user database. The applications were originally being developed with separate login for each, but I decided it would be better to share the login code across them. I investigated some ways to achieve sharing a ...