<asp:image id="Image2" runat="server" ImageUrl="ValidateCode.aspx">
ValidateCode.aspx文件的代码为： Private Sub Page_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load list() End Sub Function list() '在此处放置初始化页的用户代码 'rndnum是一个自定义函数 Dim vnum As String = rndnum(4) Session("vnum") = vnum validatecode(vnum) End Function '生成图象验证码函数 Sub validatecode(ByVal vnum) Dim img As System.drawing.Bitmap Dim g As Graphics Dim r As Random = New Random Dim gheight As Integer = Int(Len(vnum) * 13) ''gheight为图片宽度,根据字符长度自动更改图片宽度 img = New Bitmap(gheight, 20) g = Graphics.FromImage(img) 'g.DrawString(vnum, New System.Drawing.Font("Arial", 10), New System.Drawing.SolidBrush(Color.Blue), 3, 3) '新增，修改 '画图片的背景噪音线 'For i As Integer = 0 To 25 For i As Integer = 0 To 10 Dim x1 As Integer x1 = r.Next(img.Width) Dim x2 As Integer = r.Next(img.Width) Dim y1 As Integer = r.Next(img.Height) Dim y2 As Integer = r.Next(img.Height) g.DrawLine(New Pen(Color.Silver), x1, y1, x2, y2) Next i Dim font As font font = New System.Drawing.Font("Arial", 12) Dim brush As System.Drawing.Drawing2D.LinearGradientBrush brush = New System.Drawing.Drawing2D.LinearGradientBrush(New Rectangle(0, 0, img.Width, img.Height), Color.Blue, Color.Blue, 1.2F, True) g.DrawString(vnum, font, brush, 2, 2) ''画图片的前景噪音点 'For ii As Integer = 0 To 100 ' Dim x As Integer = r.Next(img.Width) ' Dim y As Integer = r.Next(img.Height) ' img.SetPixel(x, y, Color.FromArgb(r.Next())) 'Next '画图片的边框线 g.DrawRectangle(New Pen(Color.Silver), 0, 0, img.Width - 1, img.Height - 1) '在矩形内绘制字串（字串，字体，画笔颜色，左上x.左上y） Dim ms1 As System.IO.MemoryStream ms1 = New System.IO.MemoryStream img.Save(ms1, System.Drawing.Imaging.ImageFormat.Png) Response.ClearContent() '需要输出图象信息 要修改HTTP头 Response.ContentType = "image/Png" Response.BinaryWrite(ms1.ToArray()) g.Dispose() img.Dispose() Response.End() End Sub '-------------------------------------------- '函数名称:rndnum '函数参数:vcodenum--设定返回随机字符串的位数 '函数功能:产生数字和字符混合的随机字符串 '-------------------------------------------- Function rndnum(ByVal vcodenum) 'Dim vchar 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,W,X,Y,Z" Dim vchar As String = "2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,J,K,L,N,P,Q,R,S,T,U,X,Y,Z" Dim vcarray() As String = Split(vchar, ",") '将字符串生成数组 Dim vnum As String = "" Dim i As Byte For i = 1 To vcodenum Randomize() 'vnum = vnum & vcarray(Int(35 * Rnd())) '数组一般从0开始读取，所以这里为35*rnd vnum = vnum & vcarray(Int(29 * Rnd())) '数组一般从0开始读取，所以这里为35*rnd Next Return vnum End Function
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