Web Accessibility - CAPTCHA
What is it?
Those squiggly letters that machines can't read that you are asked to put in
forms to confirm that you are a human entering the form and not a bot.
CAPTCHAs are used to prevent bots from using various types of computing
services or collecting certain types of personal and sensitive information
from the computers such as gathering e-mail addresses for spamming or
ordering hundreds of tickets to a concert.
What does it stand for?
Completely Automated Public Turning test to tell Computers and Humans Apart
Frequently, a CAPTCHA features an image file of slightly distorted
alphanumeric characters. A human can typically understand the characters in
the image without too much trouble. A bot program is able to identify that
the content contains an image, but it can not see the actual image.
The image above is an example of a CAPTCHA program called E-Z Gimpy. It is
one of the most commonly used CAPTCHAs, which unfortunately has made it the
easiest to crack by using a dictionary attack.
Some CAPTCHAs now use pictures instead of words where the user is presented
with a series of pictures and asked what the common element among all of the
pictures is. By entering that common element, the user validates the
operation and the computer knows it is dealing with a human and not a bot.
Math CAPTCHAs are very popular on blog software. A Math CAPTCHA uses numbers
as an alternative to letters and asks the user to solve a simple mathematical calculation (5+3=) and type in the answer. Mathematical
equations have proven to provide a higher level of accessibility for
visually impaired users than the image-based CAPTCHAs. These are sometimes
referred to as MAPTCHAs (M = 'Mathematical'). However, these may be
difficult for users with a cognitive disorder.
To make CAPTCHAs accessible for the visually-impaired, some CAPTCHAs use
audio files where the human listens to a sequence of letters or short words
and types what they hear to show they are not a bot. While providing an
audio CAPTCHA allows visually-impaired users to hear the text, it still
presents accessibility problems for those who are both visually and hearing
impaired.
Stay tuned for the next newsletter article that will cover more on
accessibility issues with CAPTCHA.
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