Secure CAPTCHA Generator for ASP.NET

ADCaptcha.dll is a powerful CAPTCHA generation library designed for ASP.NET web applications. Safeguard your website from automated bots and spam by seamlessly integrating ADCaptcha.dll. Generate unique and customizable CAPTCHA images with distortion techniques to ensure user interactions while protecting your data from malicious activities. (Download ADCaptcha.dll)

To import the ADCaptcha.dll into an ASP.NET project after providing the download link, follow these steps:

1. Download ADCaptcha.dll: Provide a download link to the ADCaptcha.dll file on your website or any other platform where users can access it.

2. Add ADCaptcha.dll to Project: After downloading the ADCaptcha.dll, you need to add it to your ASP.NET project's references.

   • Right-click on the "References" node in your project's Solution Explorer.

   • Choose "Add Reference."

   • Click the "Browse" button and locate the downloaded ADCaptcha.dll file.

   • Select the ADCaptcha.dll file and click "Add" to add it to the project's references.

3. Import ADCaptcha Namespace: In the files where you want to use the ADCaptcha library, import the required namespaces.

   For example, if your ADCaptcha.dll has the namespace ADCaptcha, import it in the code files where you use the CAPTCHA functionalities:

   using ADCaptcha; // Import the ADCaptcha namespace.

4. Utilize the ADCaptcha Library: Now that you have imported the ADCaptcha namespace, you can use the CAPTCHA functionalities provided by the ADCaptcha.dll in your code. For example:

   using ADCaptcha;
   
   // ... (other code)
   
   // Generate a new CAPTCHA text and image.
   
   string captchaText = CaptchaGenerator.GenerateRandomText(6, DifficultyMode.Medium);
   
   byte[] captchaImageBytes = CaptchaGenerator.GenerateCaptchaImage(captchaText, 200, 60, 30, Color.White, Color.DarkBlue, DistortionTechnique.Warp, DistortionTechnique.NoiseLines);
   
   // ... (other code)

By following these steps, you can successfully import the ADCaptcha.dll into your ASP.NET project and leverage its CAPTCHA generation and verification capabilities to secure your website from automated bots and spam.

How to generate a CAPTCHA image and verify user input

Below are example usages and sample code for the ADCAPTCHA DLL. We will demonstrate how to generate a CAPTCHA image in an ASP.NET web form and how to verify user input against the CAPTCHA text.

Generating and Displaying a CAPTCHA Image (ASP.NET Web Form)

In your ASP.NET web form (e.g., CaptchaPage.aspx), add an Image control to display the CAPTCHA image:

<asp:Image ID="CaptchaImage" runat="server" />
<asp:TextBox ID="UserInputTextBox" runat="server" CssClass="form-control mt-2"></asp:TextBox>
<asp:Button ID="SubmitButton" runat="server" Text="Submit" OnClick="SubmitButton_Click" CssClass="btn btn-info mt-2" />
<%--For Testing Purpose Only DLL By ASHOK DUDI--%>
<asp:Label Text="" ID="lblMsg" runat="server" />

In the code-behind file (CaptchaPage.aspx.cs), add the following code:

using ADCaptcha;

Add the below code to Page_Load event

if (!IsPostBack)
{
    // Generate a new CAPTCHA text (You can also store this in session for verification later).
    string captchaText = CaptchaGenerator.GenerateRandomText(6, DifficultyMode.Medium);

    // Generate the CAPTCHA image and convert it to a base64 string.
    byte[] captchaImageBytes = CaptchaGenerator.GenerateCaptchaImage(captchaText, 200, 60, 24, System.Drawing.Color.White, System.Drawing.Color.DarkBlue,DistortionTechnique.NoiseLines,DistortionTechnique.Swirl, DistortionTechnique.Warp);
    // You can use anyone as required. Generate the CAPTCHA image and convert it to a base64 string.
    //byte[] captchaImageBytes = CaptchaGenerator.GenerateCaptchaImage(captchaText, 200, 60);
    string captchaImageBase64 = Convert.ToBase64String(captchaImageBytes);

    // Set the CAPTCHA image source to the base64 string.
    CaptchaImage.ImageUrl = "data:image/png;base64," + captchaImageBase64;
    CaptchaImage.BorderColor = System.Drawing.Color.DarkBlue;
    CaptchaImage.BorderWidth = 1;

    // Store the CAPTCHA text in a session for verification during form submission.
    Session["CaptchaText"] = captchaText;
}

To verify Captcha, use the below code on SubmitButton_Click event

protected void SubmitButton_Click(object sender, EventArgs e)
{
    lblMsg.Text = "";
    // Retrieve the stored CAPTCHA text from the session.
    string captchaText = Session["CaptchaText"] as string;

    // Retrieve the user's input from the TextBox.
    string userInput = UserInputTextBox.Text;

    // Verify the user's input against the CAPTCHA text (case-insensitive comparison by default).
    bool isCaptchaValid = CaptchaVerifier.VerifyCaptcha(captchaText, userInput,false);

    if (isCaptchaValid)
    {
        // CAPTCHA verification successful.
        // Proceed with the form submission or any other action.
        // ...
        lblMsg.Text = "Success";
        // Optionally, you can remove the CAPTCHA text from the session to prevent reuse of the same CAPTCHA.
       Session.Remove("CaptchaText");
    }
    else
    {
        lblMsg.Text = "Failed";
        // CAPTCHA verification failed.
        // Show an error message to the user and ask them to try again.
        // ...
    }
}

Remember to adjust the code and styling to match your specific ASP.NET project structure and design. Additionally, ensure that you have properly set up the session state in your ASP.NET application to store and retrieve the CAPTCHA text for verification.