Here I show you steps to implement captcha in your webpages
1. Add line to your .aspx file:
<%@ Register Assembly="MSCaptcha" Namespace="MSCaptcha" TagPrefix="cc1" %>
2. Where needed, add the control itself:
<cc1:CaptchaControl ID="ccJoin" runat="server" CaptchaBackgroundNoise="none" CaptchaLength="5" CaptchaHeight="60" CaptchaWidth="200" CaptchaLineNoise="None" CaptchaMinTimeout="5" CaptchaMaxTimeout="240" />
3. Put a textbox somewhere in your page where your user must enter what he sees in your captcha. Put this code (this example is in C#) to validate user input:
ccJoin.ValidateCaptcha(txtCap.Text);
if (!ccJoin.UserValidated)
{
//Inform user that his input was wrong ...
return;
}
In this particular example the ccJoin is the name of the Captcha control, the txtCap is the textbox where user entered what he sees in Captcha.
Example would produce captcha looking like that: An example of how captcha may look
Essential parameters:
- CaptchaBackgroundNoise - either "none", "low", "medium", "high" or "extreme" - the amount of noise to add to the picture to make it harder for OCR ("optical character recognition") software to recognize. Beware that this also affects how your users will be able to read and understand its content. So our recommendation is to set it to "none" and only increase the level if you'll notice the presence of automatically registered bots on your site.
- CaptchaLength - how many symbols captcha will contain. The recommended value is around 4-5, and you should increase it only if have a real problem with spammers.
- CaptchaHeight and CaptchaWidth - the height and width (in pixels) of the generated image.
- CaptchaLineNoise - adds lines to your image to further harden the OCR software work. The recommended starting value is "None", although you can increase it later.
- CaptchaMaximeout - timeout in seconds, after which your current captcha will become invalid. It is recommended to keep this value relatively high and refresh (using AJAX, for example) your captcha when it is about to become invalid.
- CaptchaMinTimeout - minimal time period in seconds for filling the captcha response. This means - if you set the CaptchaLength to 5 seconds, any input entered in first 5 seconds after Captcha's generation will be rejected.
- CaptchaChars - the string of characters to be used for Captcha generation. The default is "ABCDEFGHJKLMNPQRSTUVWXYZ23456789". We recommend to avoid using chars like O, 0, 1 and I because using different fonts they may confuse your users.