Image-Based Bot Detector is a variant of image-based CAPTCHAs that uses human ability to recognize a distorted region on the image he never seen before.
In order to use it you have to set TemplateImageFolder property to relative virtual path of the template images folder - for example, "~/templates" and to add registration of HttpHandler in web.config.
<httpHandlers>
<add verb="GET" path="ImageBasedBotDetector.ashx"
type="Marss.Web.UI.Controls.ImageBasedBotDetector, Marss.Web"/>
</httpHandlers>
There are 3 types of predefined distortion (Stretched, Random, Volute) and user-defined (Custom) distortion. In order to use predefined distortion it needs to set DistortionType property. User-defined distortion can be used in derived classes with overriden DrawCustom method.
If you want to use template images that are placed elsewhere then a subfolder of your web application - for example, from database - you have to override GetTemplateImage method.
To check whether user passed the test IsValid property is used. Also user can be locked after a predefined number of unsuccessful attempts to pass the test (FailedAttemptsBeforeLocking property, default value is 5).
Requires .NET Framework 2.0
Working example of Image-Based Bot Detector.
Working example of the control derived from Image-Based Bot Detector.
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| Public properties |
TemplateImageFolder |
Gets or sets template image folder. |
FailedAttemptsBeforeLocking |
Gets or sets the number of unsuccessful attempts before locking. |
IsValid |
Gets result of test passing. |
IsLocked |
Gets or sets value indicating where user is locked. |
DistortionType |
Gets or sets distortion type. Available types:
- Stretched - image within distorted area is stretched.
- Random - points within distorted area is mixed in a random way.
- Volute - image within distorted area is volute.
- Custom - custom distortion. Have to be used together with overriden DrawCustom method.
|
| Public events |
Locked |
Occurs when detector has been locked because of exceeding the failed attempts limit.
public event EventHandler Locked |
| Protected virtual methods |
GetTemplateImage |
Gets template image.
protected virtual System.Drawing.Image GetTemplateImage()
See example of usage. |
DrawCustom |
Distorts specified rectangle of image in a user defined way. Have to be used coupled with DistortionType=Custom
protected virtual void DrawCustom(System.Drawing.Bitmap bitmap, System.Drawing.Image img, Rectangle distortedRectangle)
where
bitmap - the output image,
img - the template (input) image,
distortedRectangle - area on the image to be distorted. |