Why use text-based CAPTCHA logic questions?
CAPTCHAs are often applied during online membership sign-up to check that the process is being undertaken by a human person rather than a (spam)-"bot". Usually, the CAPTCHA is implemented by displaying an image containing distorted words that the user has to identify. The letters are distorted so that they cannot be recognised by OCR software. ReCAPTCHA is an example of an alternative web service that offers such image CAPTCHAs.
An image based CAPTCHA from ReCAPTCHA.
Although such image CAPTCHAs are widespread, they bring a number of problems:
- The image challenge is inaccessible to visually impaired users. This problem is usually addressed by providing an alternative audio CAPTCHA for these users. However, many audio CAPTCHAs can be difficult to hear even to those with good hearing due to background noise and distorted pronunciation. This distortion is necessary in order to prevent the audio being understood by automated agents.
- Providing both image and audio CAPTCHAs is difficult to implement. ReCAPTCHA can simplify the process, but requires Javascript, and needs to be imbedded in your mark-up using iframes. Ugly.
- Image CAPTCHAs are not infallible. A number of projects have shown that automatic character recognition software can often read the letters in the image.
The W3C has witten a paper about the inaccessibility of current CAPTCHAs, and additional comments have been made by the RNIB and web leaders 456 Berea St. In such articles, the use of logic questions are suggested as a more accessible CAPTCHA test. The use of logic questions is often accused of being flawed because it is difficult to generate such questions automatically. This site undertakes this task for you and maintains a library of 157,500,799 questions. Our questions are designed to make it difficult to parse the answer from the text automatically.
There are some disadvantages to a logic question approach:
- It is probably true that text-based CAPTCHAs are less "secure" (i.e. easier to break) than their image/audio counterparts. However, all CAPTCHAs are vunerable to human sweatshop relay attacks and should form only a first line of defence.
- While entirely accessible to visually impaired users, logic questions require greater cognitive ability than image CAPTCHAs. The questions generated on this site are aimed at a child's age of 7, so should be easily possible for most adults, but may be difficult for those with a cognitive impairment.
- The logic questions are language specific. Currently this site only offers english (UK) logic questions. This problem is shared by audio CAPTCHAs, and image CAPTCHAs that use real words rather than a random sequence of letters.
So, there are the arguments: your choice! This site generates logic questions for you if you want. Peruse some examples of the questions that are generated. Find out how our service works, and sign up for your own account!