生成图象验证码函数

Sub ValidateCode(ByVal VNum As String)

Dim Img As System.Drawing.Bitmap

Dim g As Graphics

Dim ms As System.IO.MemoryStream

''gheight为图片宽度,根据字符长度自动更改图片宽度

Dim gheight As Integer = Int(Len(VNum) * 11.5)

''创建一个宽度已定，高度为20的图像

Img = New Bitmap(gheight, 20)

g = Graphics.FromImage(Img)

''在矩形内绘制字串（字串，字体，画笔颜色，左上x.左上y）

g.DrawString(VNum, (New Font("宋体", 12)), (New SolidBrush(Color.Blue)), 3, 3)

ms = New System.IO.MemoryStream

Img.Save(ms, 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(ms.ToArray())

g.Dispose()

Img.Dispose()

Response.End()

End Sub