[TuToRiAl] How to make Offline (No Internet) Captcha (Human Confirmation) [TuToRiAl]

A CAPTCHA or Captcha (pronounced /ˈkæptʃə/) is a type of challenge-response test used in computing to ensure that the response is not generated by a computer. The process usually involves one computer (a server) -- WOW, WOW, WOW. A SERVER??? |||||| asking a user to complete a simple test which the computer is able to generate and grade.

Welcome to my tutorial on how to generate Captcha without using pictures, internet connection or anything external that the application has to access; as long as you get a human response? Correct? I believe so. Today I will show you a nice feature that almost every computer can do in the world, generate a random number!... -.-'

We will be using that method in our captcha, and the best part about offline captcha in a VB form my way, is that there is NO need to refresh it for the following reasons:

Unreadable Letters
Long and Pointless Words
Never loaded correctly
Half the Captcha loaded

_____________________________________________

Code:

Public Class Form1

    Dim charactersDisallowed As String = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ,<>./?; :'{}[]=+-_)(*&^%$#@!~`|\uç▲ìα▲╜KÄ╤ZlÆ╘¦«¨©÷ ¢¡¬®¯°±²³´µ¶·¸¹£¤¥»¼½¾¿"

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

        KeyPreview = True

        Try

            Dim Random As New Random

            TextBox1.Text = Random.Next(TextBox2.Text)

        Catch ex As Exception

            MsgBox("Invalid Characters/No Numerical Value Detected", 16, "Fatal Error")

        End Try

        TextBox2.Visible = False 'This is what gives a digit limit for random captcha.

TextBox1.Enabled = False 'Disables TextBox so User cannot copy and paste the captcha.

        TextBox1.ReadOnly = True 'Disables so user cannot edit the captcha.

    End Sub

Code:

Dim Random As New Random

        TextBox1.Text = Random.Next(TextBox2.Text)

Code:

If TextBox3.Text = TextBox1.Text Then

            MsgBox("Captcha entered successfuly!", 64, "Human Detected!")

            'Other Code should be put here if the user enters the captcha correctly, like Form2.Show()

        Else

            MsgBox("Your Kind is Not wanted Here, Robot!", 48, "Robot Detected!")

            'here add code that tells the user they have entered it incorrectly, I called them a robot for fun.

        End If

Code:

Dim theText As String = TextBox3.Text

        Dim Letter As String



        For x As Integer = 0 To TextBox3.Text.Length - 1

            Letter = TextBox3.Text.Substring(x, 1)

            If charactersDisallowed.Contains(Letter) Then

                theText = theText.Replace(Letter, String.Empty)

            End If

        Next

        TextBox3.Text = theText

        TextBox3.Select(TextBox3.Text.Length, 0)

Code:

Private Sub TextBox3_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox2.KeyDown

        If e.KeyCode = Keys.Enter Then

            Button3_Click(Nothing, Nothing)

        End If

    End Sub

Code:

Public Class Form1

    Dim charactersDisallowed As String = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ,<>./?; :'{}[]=+-_)(*&^%$#@!~`|\uç▲ìα▲╜KÄ╤ZlÆ╘¦«¨©÷ ¢¡¬®¯°±²³´µ¶·¸¹£¤¥»¼½¾¿"

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

        KeyPreview = True

        Try

            Dim Random As New Random

            TextBox1.Text = Random.Next(TextBox2.Text)

        Catch ex As Exception

            MsgBox("Invalid Characters/No Numerical Value Detected", 16, "Fatal Error")

        End Try

        TextBox2.Visible = False 'This is what gives a digit limit for random captcha.

        TextBox1.Enabled = False 'Disables TextBox so User cannot copy and paste the captcha.

        TextBox1.ReadOnly = True 'Disables so user cannot edit the captcha.

    End Sub



    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click

        Dim Random As New Random

        TextBox1.Text = Random.Next(TextBox2.Text)

    End Sub



    Private Sub TextBox3_KeyDown(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles TextBox2.KeyDown

        If e.KeyCode = Keys.Enter Then

            Button3_Click(Nothing, Nothing)

        End If

    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click

        If TextBox3.Text = TextBox1.Text Then

            MsgBox("Captcha entered successfuly!", 64, "Human?")

            'Other Code should be put here if the user enters the captcha correctly, like Form2.Show()

        Else

            MsgBox("Your Kind is Not wanted Here, Robot!", 48, "Robot Detected!")

            'here add code that tells the user they have entered it incorrectly, I called them a robot for fun.

        End If

    End Sub



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

        End

    End Sub



    Private Sub TextBox3_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox3.TextChanged

        Dim theText As String = TextBox3.Text

        Dim Letter As String



        For x As Integer = 0 To TextBox3.Text.Length - 1

            Letter = TextBox3.Text.Substring(x, 1)

            If charactersDisallowed.Contains(Letter) Then

                theText = theText.Replace(Letter, String.Empty)

            End If

        Next

        TextBox3.Text = theText

        TextBox3.Select(TextBox3.Text.Length, 0)

    End Sub

End Class