Captcha text in VB.NET

Captcha is one of the way through which the unknown visitors or the hackers will be prevented with great ease.

This topics contains the example program of Captcha text in VB.NET. The CAPTHA stands for Completely Automated Public Turing test to tell Computers and Humans Apart. This will reduce the hackers, spam attackers, and fake visitors or entries from website.

Example Screenshot: In the following example we create one label to display random generated captcha text, Refresh button to change captcha text, Text box to enter captcha text for trusted users and Register button to verify the entered text valid or not.

Captcha text in VB.NET

Source Code :

System.Drawing.Drawing2D is the two dimensional and vector graphics functionality. The randomly generated captcha text stores in str string variable. In the button it validates txtReg text box and str variable. The random generated text stores in str variable. Maimum it stores 5 characters. The the program converts text to bit map image. Same code applied in the form load and btn referesh button.

Imports System.Drawing.Drawing2D
Public Class Form1
    Dim str As String
    Private Sub btnShow_Click(sender As Object, e As EventArgs) Handles btnReg.Click
        If txtReg.Text = str Then
            MsgBox("Register Success")
        Else
            MsgBox("Register Faile")
        End If
    End Sub

    Private Sub btnRefresh_Click(sender As Object, e As EventArgs) Handles btnRefresh.Click
        Dim NumCaptcha As String = "123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
        str = ""
        Dim R As New Random
        For i As Integer = 0 To 5
            str = str + NumCaptcha(R.Next(0, 60))
        Next
        Dim b As New Bitmap(274, 71, Imaging.PixelFormat.Format32bppArgb)
        Dim g As Graphics = Graphics.FromImage(b)
        Dim Hb As New HatchBrush(HatchStyle.DottedDiamond, Color.FromArgb(255, 128, 0), Color.Black)
        g.DrawString(str, New Font("Curlz MT", 40, FontStyle.Strikeout, GraphicsUnit.Point), Brushes.White, 5, 5)
        picCaptcha.Image = b
    End Sub

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Dim NumCaptcha As String = "123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
        str = ""
        Dim R As New Random
        For i As Integer = 0 To 5
            str = str + NumCaptcha(R.Next(0, 60))
        Next
        Dim b As New Bitmap(274, 71, Imaging.PixelFormat.Format32bppArgb)
        Dim g As Graphics = Graphics.FromImage(b)
        Dim Hb As New HatchBrush(HatchStyle.DottedDiamond, Color.FromArgb(255, 128, 0), Color.Black)
        g.DrawString(str, New Font("Curlz MT", 40, FontStyle.Strikeout, GraphicsUnit.Point), Brushes.White, 5, 5)
        picCaptcha.Image = b
    End Sub
End Class

Project title: Captcha text in VB.NET
Programming Language: VB.NET

The applications of using CAPTCHA are as follows:

  • Prevent spam: This application will help prevention of spam comment in blogs.
  • Website registration: This will help in protecting the websites during the registration process.
  • Differentiate: The CAPTCHA will help in differentiating between the humans and the robots with great ease.
  • Email address: The CAPTCHA will also help in protecting the email addresses from the scrapers.
  • Dictionary attacks: This can also help in preventing the dictionary attacks without any difficulty.
  • Online polling: This can also help in detecting whether the vote casted through online is by a human or a robot.
  • Web pages: This will help in protecting the confidential information of the web pages.
  • Prevent bots: The CAPTCHA can help in preventing the bots that will be used in the social networking sites or during some form registration.

Download Example Code:

download

Video Tutorial of Captcha Text:

Anu

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