VB.net 产生随机验证码

Imports System.Drawing
Imports System.Drawing.Imaging
Imports System.Drawing.Drawing2D
Partial Class _Default
    Inherits System.Web.UI.Page

    Dim path As String

    '產生隨機字串
    Private Function GenCode(ByVal num As Integer) As String
        Dim [source] As String() = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"}
        Dim code As String = ""
        Dim rd As Random = New Random()
        Dim i As Integer
        For i = 0 To num - 1 Step i + 1
            code += source(rd.Next(0, source.Length))
        Next
        Return code
    End Function

    '生成圖片
    Private Sub GenImg(ByVal code As String)
        Dim myPalette As Bitmap = New Bitmap(60, 18) '定義一個畫板

        Dim gh As Graphics = Graphics.FromImage(myPalette) '在畫板上定義繪圖的實例

        Dim rc As Rectangle = New Rectangle(0, 0, 60, 18) '定義一個矩形

        gh.FillRectangle(New SolidBrush(Color.DarkSeaGreen), rc) '填充矩形
        gh.DrawString(code, New Font("Arial", 12), New SolidBrush(Color.White), rc) '在矩形內畫出字串

        myPalette.Save(Request.MapPath(path) + "\1.bmp", System.Drawing.Imaging.ImageFormat.Jpeg) '將圖片顯示出來

        Session("Code") = code '將字串保存到Session中，以便需要時進行驗證

        gh.Dispose()
        myPalette.Dispose()
    End Sub

    '生成圖片（增加背景噪音線、前景噪音點）
    Private Sub CreateCheckCodeImage(ByVal checkCode As String)
        If checkCode = Nothing Or checkCode.Trim() = String.Empty Then
            Return
        End If

        Session("Code") = checkCode '將字串保存到Session中，以便需要時進行驗證

        Dim image As System.Drawing.Bitmap = New System.Drawing.Bitmap(CType(Math.Ceiling((checkCode.Length * 12.5)), Integer), 22)
        Dim g As Graphics = Graphics.FromImage(image)

        Try
            '生成隨機生成器
            Dim random As Random = New Random()

            '清空圖片背景色
            g.Clear(Color.White)

            '畫圖片的背景噪音線
            Dim i As Integer
            For i = 0 To 25 - 1 Step i + 1
                Dim x1 As Integer = random.Next(image.Width)
                Dim x2 As Integer = random.Next(image.Width)
                Dim y1 As Integer = random.Next(image.Height)
                Dim y2 As Integer = random.Next(image.Height)

                g.DrawLine(New Pen(Color.Silver), x1, y1, x2, y2)
            Next

            Dim font As Font = New System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold))
            Dim brush As System.Drawing.Drawing2D.LinearGradientBrush = New System.Drawing.Drawing2D.LinearGradientBrush(New Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2F, True)
            g.DrawString(checkCode, font, brush, 2, 2)
            Session("checkCode") = checkCode

            '畫圖片的前景噪音點
            Dim j As Integer
            For j = 0 To 100 - 1 Step j + 1
                Dim x As Integer = random.Next(image.Width)
                Dim y As Integer = random.Next(image.Height)

                image.SetPixel(x, y, Color.FromArgb(random.Next()))
            Next
            '畫圖片的邊框線
            g.DrawRectangle(New Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1)

            Dim ms As System.IO.MemoryStream = New System.IO.MemoryStream()
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif)
            Response.ClearContent()
            Response.ContentType = "image/Gif"
            Response.BinaryWrite(ms.ToArray())
        Finally
            g.Dispose()
            image.Dispose()
        End Try
    End Sub

    Protected Sub Login1_Authenticate(ByVal sender As Object, ByVal e As System.Web.UI.WebControls.AuthenticateEventArgs) Handles Login1.Authenticate

        If (Login1.UserName = "1" And Login1.Password = "2") Then
            If Me.TextBox1.Text = Session("Code") Then
                e.Authenticated = True
            Else
                e.Authenticated = False
                Me.Label1.Text = "不成功"
            End If
        End If

    End Sub

    Protected Sub ImageButton1_Click(ByVal sender As Object, ByVal e As System.Web.UI.ImageClickEventArgs) Handles ImageButton1.Click
        ' GenImg(GenCode(4))

    End Sub

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        '  CreateCheckCodeImage(GenCode(4))

   
    End Sub

    Protected Sub Button1_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles Button1.Click
        GenImg(GenCode(4))
        Me.Label1.Text = Session("Code")
    End Sub
End Class