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