The word Captcha is an abbreviation used for Completely Automated Public Turing Test to Tell Computers and Humans Apart.
They are used on many websites as a means to verify your identity.
They are seen as as obscured letters and numbers in an image.
One form that everyone is familiar with is the scrambled text version.
Others include simple questions, simple questions and sometimes include image selection where the user is required to find images of something shown out of other images.
Uses of captcha
Captcha are used to check if robots or humans are submitting forms, creating accounts and spamming.
This done by having a robot sign up for multiple unwanted email accounts and accounts for registering at forums to spam people. They also prevent robots from gaining access to websites and web apps.
The positive and negative effects of using captcha
Captchas are not always effective against robots because there are ways and means available that can to make robots to read and extract the text of images thus rendering a Captcha useless.
Captchas do not work when it comes to people who are blind and the disabled.
Although there are audio Captchas available, it is difficult for disabled people to understand what the Captcha is saying. In fact, even normal people find it difficult to make sense of these captchas.
CAPTCHAs are designed to in such a manner that it assumes that all responses are made by computers.
A CAPTCHA that allows you to respond after hearing the audio words is not very helpful when it comes to someone with poor hearing and eyesight. The result will be that the Captcha will consider their response to be incorrect and prevent them from going any further.
Captchas can be used to stop spammers only if all other methods have failed to produce the desired results.
You will find that robots gather input data into form fields by going through the page, finding the inputs names, matching and placing the data in the values of those fields.
Robots do not read the type of input but rather find the name and then change the values, so as a precautionary measure what you can do is have the system check to see if any changes have been made. Although there is no guarantee that this method works, it is better to be safe than sorry.
How to verify form submission
Unlike humans who are slow to fill up forms, robots can fill up details and submit forms without much time lost. In order to combat combat spam robots effectively, you need to check how quickly the forms get submitted by keeping a track of IP addresses that were used and when was the last time that someone from that particular IP address submitted the form.
Again, this method is not very effective, as some organizations and companies maybe using more than IP addresses which would give unreliable results.
Direct submission of forms
Another thing you need to do is check if there is direct access to form handler scripts so that it tells you more about the the referrer and you can confirm that the submission of a form is coming from a page on your website.
As stated earlier, there are other ways of preventing robots from making form submissions. The problem is that no mehod is completely reliable when it comes to spam prevention but captchas have proven to be effective so far in reducing if not eliminating spam by creating enough ways to verify if the forms are indeed being submitted by robots.
The challenge is in making Captchas effective in such a way that they are able to tell the difference between a human response and a response that is made by a robot during form submission. Only then can we say that captchas have really worked.