Wesites capture lot of data from their users in form of comments, surveys, signups and other ways of feedback. This helps site owners remain in contact with their customers, visitors or readers, analyze their trends and publish better content. However as this trend grows, the problem of spamming a site with automated scripts (bots) has proliferated, this hinders capturing of useful genuine data that website owner requires to reach its audience. To fight this problem, new techinques have been evolved and best of them is the image verification technique called as captcha.
Your form presents your visitors with an image having a security code drawn on it in a sufficently readable format. Your users need to identify the code and input the correct code inside a textbox, given generally below the security code image, while submitting the form on your website. Your script accepts the data and saves it into database or emails you the information ONLY if the security code entered by the user matches to the security code that was shown in the image to the user. Since automated scripts cannot read image and therefore the security code inside the image, it prevents the spam attacks on your site by such automated bots. Only humans can read and identify an image, is the base of this technique.
There have been some readymade scripts already available on the net that enables you to deploy a captcha image on your website forms. However such scripts have additional requirements like for example, stylish fonts, image libraries enabled on your servers. Besides such scripts provide only an image captcha, however if your website audience have been users with poor eye sights or if you wish that your site/form is accessible to all types of users then, only an image captcha won’t be sufficent. Low sighted people may not be able to fill in the correct security code and therefore they may not be able to post their data on your website and as result you might be missing some valuable information. For such users an audio captcha is a good alternative, where they can hear the security code and input in your website form while submitting the data. However such audio captchas are difficult to implement.
To address all these problems Re-Captcha has implemented a wonderful free anti-bot service. This service is absolutely free, and through this service you can show a captcha in both image and audio format to your users. This also doesnot require any additional features enabled on your server. The service can be activated by just signing up for an account on Re-Captcha and generating an API KEY for each of your website domains in which you want to implement the captcha. Your single account can have multiple sites configured. This service is available for any kind of websites developed in any language like PHP, .NET, JAVA and many others. They have also provided a wonderful resources section giving enough examples and libraries to implement it on your site. Also when you implement the re-captcha service, it not only prevents the spam attacks on your website but also helps to digitize old texts, learn more about this.