Image-Based Bot Detector

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.

Licence

Copyright (c) 2007, Mykola Tarasyuk
All rights reserved.
Redistribution and use in source and binary forms, with or without modification, are permitted provided that the following conditions are met:
* Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
* Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.
* The name of the copyright holder may not be used to endorse or promote products derived from this software without specific prior written permission.

THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

Download Image-Based Bot Detector

Requires .NET Framework 2.0

Overview, help

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).

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.