How to create verification code to prevent auto signup in ASP.NET 2.0 (C#)?

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Verification code to prevent auto signup in ASP.NET(VB)

By entering the verification code shown on the web page when a user sign up, the web site or application can prevent automated registrations. This reduces system loads and ensures better performance and security of web site or application. This tutorial will show you how to create the randomly generated verification code in ASP.NET 2.0 and VB. In order to create a random verification code, we create a method called CreateRandomCode at first

Private Function generateVCode(ByVal CodeLength As Integer) As String

Dim VCode As String = String.Empty
Dim randObj As New Random()
Dim c As Integer = 63
For i As Byte = 1 To CodeLength

c = randObj.Next(35)
If c >= 10 Then

c += 7

End If
c += 48
VCode += Chr(c)

Next
Return VCode

End Function

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Then we generate verification code character string as exported image

Private Function generateHatchStyle() As HatchStyle

Dim slist As New ArrayList
For Each style As HatchStyle In System.Enum.GetValues(GetType(HatchStyle))

slist.Add(style)

Next

Dim randObj As New Random()
Dim index As Integer = randObj.Next(slist.Count - 1)

Return CType(slist(index), HatchStyle)

End Function

Use a method GenerateVCodeImage to print image

Private Function GenerateVCodeImage()

Dim oBitmap As Drawing.Bitmap = New Drawing.Bitmap(90, 35)
Dim oGraphic As Drawing.Graphics = Drawing.Graphics.FromImage(oBitmap)
Dim foreColor As System.Drawing.Color
Dim backColor As System.Drawing.Color

Dim sText As String = generateVCode(6)
Dim sFont As String = "Comic Sans MS"

foreColor = System.Drawing.Color.FromArgb(220, 220, 220)
backColor = System.Drawing.Color.FromArgb(190, 190, 190)

Dim oBrush As New Drawing.Drawing2D.HatchBrush(CType(generateHatchStyle(), Drawing.Drawing2D.HatchStyle), foreColor, backColor)

Dim oBrushWrite As New Drawing.SolidBrush( Drawing.Color.Red)

oGraphic.FillRectangle(oBrush, 0, 0, 100, 50)
oGraphic.TextRenderingHint = Drawing.Text.TextRenderingHint.AntiAlias

Dim oFont As New Drawing.Font(sFont, 14)
Dim oPoint As New Drawing.PointF(5.0F, 4.0F)

oGraphic.DrawString(sText, oFont, oBrushWrite, oPoint)

Response.ContentType = "image/jpeg"
oBitmap.Save(Response.OutputStream, Drawing.Imaging.ImageFormat.Jpeg)
oBitmap.Dispose()

Return sText

End Function

Transfer function on Page_load

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

Dim code As String = GenerateVCodeImage()
Session("VCode") = code

End Sub

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