Captcha Using Asp.Net

Imports System
Imports System.Collections
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Web
Imports System.Web.SessionState
Imports System.Web.UI
Imports System.Web.UI.WebControls
Imports System.Web.UI.HtmlControls
 
Imports System.Drawing.Text
Imports System.Data.OleDb
 
Partial Class _Default
    Inherits System.Web.UI.Page
 
    ''' <summary>
    ''' This function will create a bitmap from the given string and implement random changes on that bitmap to make it a capcha.
    ''' </summary>
    ''' <param name="sImageText"></param>
    ''' <returns>bitmap image</returns>
    ''' <remarks></remarks>
    Private Function CreateImage(ByVal sImageText As String)
 
        Dim bmpImage As New Bitmap(1, 1)
        Dim iWidth As Integer = 0
        Dim iHeight As Integer = 0
        Dim RandomInst As New Random
        Dim iMinNoice As Integer = RandomInst.Next(6, 9)
        Dim iMaxNoice As Integer = RandomInst.Next(9, 11)
        Dim iScrachCode As Integer = RandomInst.Next(3, 6)
        Dim iVerHorRand As Integer = RandomInst.Next(1, 4)
        Dim iColor As System.Drawing.Color = GetColorFromID(RandomInst.Next(1, 7))
        Dim i_backColor As Color = Nothing
        'Create a Font object
 
        Dim MyFont As New Font(GetRandomFontName, 30, System.Drawing.FontStyle.Bold + _
                        System.Drawing.FontStyle.Italic, System.Drawing.GraphicsUnit.Point)
 
        Dim MyGraphics As Graphics
        MyGraphics = Graphics.FromImage(bmpImage)
 
        'Resize the bitmap, this is where the bitmap is sized.
        iWidth = CInt(MyGraphics.MeasureString(sImageText, MyFont).Width)
        iHeight = CInt(MyGraphics.MeasureString(sImageText, MyFont).Height)
 
        bmpImage = New Bitmap(bmpImage, New Size(iWidth, iHeight - 1))
 
 
 
        MyGraphics = Graphics.FromImage(bmpImage)
 
        MyGraphics.Clear(Color.White)
        i_backColor = bmpImage.GetPixel(0, 0)
 
 
        MyGraphics.TextRenderingHint = TextRenderingHint.AntiAlias
        MyGraphics.DrawString(sImageText, MyFont, New SolidBrush(iColor), 0, 0)
 
        'Put random pixels on the image
        For m As Integer = 1 To iHeight - 3
            For n As Integer = 1 To iWidth - 3
                If m Mod RandomInst.Next(iMinNoice, iMaxNoice) = 0 Then
                    bmpImage.SetPixel(n, m, iColor)
                ElseIf n Mod RandomInst.Next(iMinNoice, iMaxNoice) = 0 Then
                    bmpImage.SetPixel(n, m, iColor)
                End If
            Next
        Next
 
        'draw random bars on the image
        For m As Integer = 1 To iHeight - 3
            For n As Integer = 1 To iWidth - 3
                If m Mod 10 = 0 Then
                    bmpImage.SetPixel(n, m, iColor)
                ElseIf n Mod 10 = 0 Then
                    bmpImage.SetPixel(n, m, iColor)
                End If
            Next
        Next
        'draw random graphics on the bitmap
        Select Case iVerHorRand
            Case 1
                For m As Integer = 1 To iHeight - 3
                    For n As Integer = 1 To iWidth - 3
                        If bmpImage.GetPixel(n, m) <> i_backColor AndAlso _
                            m Mod (iScrachCode * iScrachCode) = 0 Then
                            bmpImage.SetPixel(n, m, i_backColor)
                        End If
                    Next
                Next
            Case 2
                For m As Integer = 1 To iHeight - 3
                    For n As Integer = 1 To iWidth - 3
                        If bmpImage.GetPixel(n, m) <> i_backColor AndAlso _
                            n Mod (iScrachCode * iScrachCode) = 0 Then
                            bmpImage.SetPixel(n, m, i_backColor)
                        End If
                    Next
                Next
            Case 3
                iScrachCode = RandomInst.Next(4, 7)
                For m As Integer = 1 To iHeight - 3
                    For n As Integer = 1 To iWidth - 3
                        If bmpImage.GetPixel(n, m) <> i_backColor AndAlso _
                            m Mod iScrachCode = 0 AndAlso n Mod iScrachCode = 0 Then
                            bmpImage.SetPixel(n, m, i_backColor)
                        End If
                    Next
                Next
        End Select
 
        MyGraphics.Flush()
        Return bmpImage
 
    End Function
    ''' <summary>
    ''' This function will return the name of the font as per the given ID
    ''' </summary>
    ''' <param name="a_FontID"></param>
    ''' <returns>Name of the font as per the given ID</returns>
    ''' <remarks></remarks>
    Private Function GetFontNameFromID(ByVal a_FontID As Integer) As String
        GetFontNameFromID = Nothing
 
        Select Case a_FontID
            Case 1 : GetFontNameFromID = "Goudy Stout"
            Case 2 : GetFontNameFromID = "Copperplate Gothic Bold"
            Case 3 : GetFontNameFromID = "Eras Bold ITC"
            Case 3 : GetFontNameFromID = "Blue Highway Linocut"
            Case 4 : GetFontNameFromID = "Rockwell Extra Bold"
            Case 4 : GetFontNameFromID = "Eras Bold ITC"
            Case 5 : GetFontNameFromID = "Verdana"
            Case 6 : GetFontNameFromID = "Algerian"
            Case 7 : GetFontNameFromID = "Bodoni MT Black"
            Case 8 : GetFontNameFromID = "Cooper Black"
            Case 10 : GetFontNameFromID = "Gill Sans Ultra Bold"
            Case 11 : GetFontNameFromID = "Rockwell Extra Bold"
            Case 12 : GetFontNameFromID = "Showcard Gothic"
            Case 13 : GetFontNameFromID = "Berlin Sans FB Demi"
 
        End Select
 
    End Function
 
    Private Function GetCharFromID(ByVal a_CharID As Integer) As String
        GetCharFromID = " "
        'This function return a charecter according to the value of the variable "a_CharID"
        'Here some confucing letters like I,l and 1 are avoided
        Select Case a_CharID
            Case 1 To 2 : GetCharFromID = Chr(76)
 
            Case 3 To 10 : GetCharFromID = Chr(a_CharID + 47)
 
            Case 11 To 18 : GetCharFromID = Chr(a_CharID + 54)
 
            Case 19 : GetCharFromID = Chr(a_CharID + 53)
 
            Case 20 To 36 : GetCharFromID = Chr(a_CharID + 54)
 
            Case 37 To 47 : GetCharFromID = Chr(a_CharID + 60)
 
            Case 48 : GetCharFromID = Chr(a_CharID + 59)
 
            Case 49 To 63 : GetCharFromID = Chr(a_CharID + 60)
 
        End Select
    End Function
 
    ''' <summary>
    ''' Return a random color as per the color ID
    ''' </summary>
    ''' <param name="a_ColorId"></param>
    Private Function GetColorFromID(ByVal a_ColorId As Integer) As Color
        GetColorFromID = Color.Green
 
        Select Case a_ColorId
            Case 1 : GetColorFromID = Color.Green
            Case 2 : GetColorFromID = Color.Blue
            Case 3 : GetColorFromID = Color.Red
            Case 4 : GetColorFromID = Color.Violet
            Case 5 : GetColorFromID = Color.Black
            Case 6 : GetColorFromID = Color.RosyBrown
            Case 7 : GetColorFromID = Color.Brown
            Case 8 : GetColorFromID = Color.Navy
            Case 8 : GetColorFromID = Color.Plum
        End Select
 
    End Function
    ''' <summary>
    ''' This function will generate a random string with length of a_Length
    ''' </summary>
    ''' <param name="a_Length"></param>
    Private Function GetRandomString(ByVal a_Length As String) As String
        GetRandomString = ""
        Dim RandomInst As New Random
        'GetCharFromID() function will returns 63 different charecters according 
        'to the ID passing to the function. Here we are calling the function 5 times 
        'with a random number as ID and thus creating a charecter string with 5 
        'random charecters.
 
        For i As Integer = 1 To a_Length
            GetRandomString = GetRandomString + GetCharFromID(RandomInst.Next(1, 63)) '+ " "
        Next
    End Function
 
    Private Function GetRandomFontName() As String
        GetRandomFontName = ""
        Dim RandomInst As New Random
        GetRandomFontName = GetFontNameFromID(RandomInst.Next(1, 13))
 
    End Function
 
 
    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        Response.ContentType = "image/gif"
        Dim bmpImage As New Bitmap(1, 1)
        Dim strImage As String = GetRandomString(5) 'Create a random string with the length of 5 charecter
 
        'Call the CreateImage() function to save the random string to a stream which will be
        'drawn in the CreateImage() function.
        bmpImage = CreateImage(strImage)
        Dim a As String = ""
        bmpImage.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Gif)
        Response.End()
    End Sub
End Class