网页注册验证码如何生成和怎么刷新啊

网页注册验证码怎么生成和如何刷新啊？？
网页注册验证码怎么生成和如何刷新啊？？

[解决办法]
生成用服务端语言，比如以下是我用asp.net/vb写的

VB.NET code

Imports System.IOImports System.DrawingImports System.Drawing.ImagingPartial Class getpassimgcode    Inherits System.Web.UI.Page    Dim rand As New Random()    Dim r As Byte, g As Byte, b As Byte    Dim imagebackgroundbrightness As Byte = 162     Function gethightcontrastcolor(Optional ByVal brightness1 As Byte = 255, Optional ByVal dif As Byte = 60) As Color        r = rand.Next(0, 256)        g = rand.Next(0, 256)        b = rand.Next(0, 256)        While Math.Abs(getcolorbrightness(r, g, b) - brightness1) < dif            r = rand.Next(0, 256)            g = rand.Next(0, 256)            b = rand.Next(0, 256)        End While        Return Color.FromArgb(r, g, b)    End Function    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load        Dim VNum As String = Right(Rnd().ToString, 5)        Session("VNum") = VNum        If Not Request.UrlReferrer Is Nothing AndAlso Request.UrlReferrer.ToString.IndexOf("userlogin.aspx") > -1 Then imagebackgroundbrightness = 255        ValidateCode(VNum)    End Sub    '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 MemoryStream        Dim gheight As Integer = Int(Len(VNum) * 11.5)        '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)        For i As Int16 = 1 To Len(VNum)            g.DrawString(Mid(VNum, i, 1), New Font("Arial", 10, FontStyle.Bold), New SolidBrush(gethightcontrastcolor(imagebackgroundbrightness)), (i - 1) * 10 + 3, 3)        Next        ms = New MemoryStream()        Img.Save(ms, 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    Function getcolorbrightness(ByVal r As Int16, ByVal g As Int16, ByVal b As Int16) As Double        Return (299 * r + 587 * g + 114 * b) / 1000    End FunctionEnd Class
[解决办法]
探讨


生成用服务器端语言生成后比如存成 getcodeimg.asp
然后调用页就可以<img src=" getcodeimg.asp" id="img1" />
刷新<a onclick=' document.getElementById("img").src = "getcodeimg.asp?" + Math.random()'>看不清？换一个<a/>