Pros and Cons of CAPTCHA Logic Questions
As you consider the use of textual-CAPTCHAs it is important to weigh their pros and cons compared to an image-based service such as ReCAPTCHA.
An image based CAPTCHA from ReCAPTCHA.
Although such image CAPTCHAs are widespread, they create problems:
- The image challenge is inaccessible to visually impaired users. This problem is usually addressed by providing an alternative audio CAPTCHA. However, most audio CAPTCHAs are difficult to understand due to background noise and distorted pronunciation which is necessary in order to prevent the audio being understood by automated agents.
- Providing both image and audio CAPTCHAs is difficult to implement, although services like ReCAPTCHA simplifies the process.
- 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.
There are disadvantages to a logic question approach:
- Text-based CAPTCHAs are definitely less "secure" (i.e. easier to break) than their image/audio counterparts: the recent evolution in natural language parsers such as Wolfram Alpha has made question solution easier.
- While accessible to visually impaired users, logic questions require greater cognitive ability than image CAPTCHAs.
- 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.
Questions? Contact Rob.