How to Create Captcha Code In Visual Studio

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Preview

Hello friends, in this post I will discuss about how to create a captcha code in a form using Visual Studio 2010 (VB.Net).

Captcha is a challenge-response test used in computing to ensure answers are not produced by computers. First open Visual Studio and create a new project, then create a form with the design as shown below

NOTES :

Components in Form:

• PictureBox
• TextBox
• Button
• Label

After that, go into the code and import some of the required libraries:

Imports System.Text
Imports System.Drawing
Imports System.Windows.Forms
Imports System.Drawing.Drawing2D  

Public Class Form1

End Class

When done, declare some global variables as needed

Public Class Form1

 Dim DrawingFont As New Font("Arial", 25)
 Dim CaptchaImage As New Bitmap(140, 40)
 Dim CaptchaGraf As Graphics = Graphics.FromImage(CaptchaImage)
 Dim Alphabet As String = "AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz"   
 Dim CaptchaString, TickRandom As String
 Dim ProcessNumber As Integer

End Class

Then, create a function for the captcha code generation process

Private Sub GenerateCaptcha()
        ProcessNumber = My.Computer.Clock.LocalTime.Millisecond
        If ProcessNumber < 521 Then
            ProcessNumber = ProcessNumber \ 10
            CaptchaString = Alphabet.Substring(ProcessNumber, 1)
        Else
            CaptchaString = CStr(My.Computer.Clock.LocalTime.Second \ 6)
        End If
        ProcessNumber = My.Computer.Clock.LocalTime.Second
        If ProcessNumber < 30 Then
            ProcessNumber = Math.Abs(ProcessNumber - 8)
            CaptchaString += Alphabet.Substring(ProcessNumber, 1)
        Else
            CaptchaString += CStr(My.Computer.Clock.LocalTime.Minute \ 6)
        End If
        ProcessNumber = My.Computer.Clock.LocalTime.DayOfYear
        If ProcessNumber Mod 2 = 0 Then
            ProcessNumber = ProcessNumber \ 8
            CaptchaString += Alphabet.Substring(ProcessNumber, 1)
        Else
            CaptchaString += CStr(ProcessNumber \ 37)
        End If
        TickRandom = My.Computer.Clock.TickCount.ToString
        ProcessNumber = Val(TickRandom.Substring(TickRandom.Length - 1, 1))
        If ProcessNumber Mod 2 = 0 Then
            CaptchaString += CStr(ProcessNumber)
        Else
            ProcessNumber = Math.Abs(Int(Math.Cos(Val(TickRandom)) * 51))
            CaptchaString += Alphabet.Substring(ProcessNumber, 1)
        End If
        ProcessNumber = My.Computer.Clock.LocalTime.Hour
        If ProcessNumber Mod 2 = 0 Then
            ProcessNumber = Math.Abs(Int(Math.Sin(Val(My.Computer.Clock.LocalTime.Year)) * 51))
            CaptchaString += Alphabet.Substring(ProcessNumber, 1)
        Else
            CaptchaString += CStr(ProcessNumber \ 3)
        End If
        ProcessNumber = My.Computer.Clock.LocalTime.Millisecond
        If ProcessNumber > 521 Then
            ProcessNumber = Math.Abs((ProcessNumber \ 10) - 52)
            CaptchaString += Alphabet.Substring(ProcessNumber, 1)
        Else
            CaptchaString += CStr(My.Computer.Clock.LocalTime.Second \ 6)
        End If
        CaptchaGraf.Clear(Color.White)

        For hasher As Integer = 0 To 5
            CaptchaGraf.DrawString(CaptchaString.Substring(hasher, 1), DrawingFont, Brushes.Black, hasher * 20 + hasher + ProcessNumber \ 200, (hasher Mod 3) * (ProcessNumber \ 200))  
        Next
        PictureBox1.Image = CaptchaImage
End Sub

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Then, double-click Button 1 to identify the text that is typed in the TextBox equal to the captcha that will appear in the PictureBox

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click  
     If TextBox1.Text = CaptchaString Then
         MsgBox("Captcha Correct", MsgBoxStyle.Information)
         TextBox1.Clear()
         GenerateCaptcha()
     Else
         MsgBox("Captcha Incorrect", MsgBoxStyle.Exclamation)
         TextBox1.Clear()
     End If
End Sub

And finally, call the function you have created into Form_Load and Button_2 click

Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click   
    GenerateCaptcha()
End Sub

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    GenerateCaptcha()
End Sub

When done and there is no error, the program is ready to run.

For more details, please watch the video below