asp生成验证码

 =========驗證串==========
<%
Option Explicit
Response.buffer=true
NumCode
Function NumCode()
    Response.Expires = -1
    Response.AddHeader "Pragma","no-cache"
    Response.AddHeader "Cache-Control","no-cache"
    On Error Resume Next
    Dim zNum,i,j
    Dim Ados,Ados1
    Randomize timer
    zNum = cint(8999*Rnd+1000)
    Session("image_check") = zNum
    Dim zimg(4),NStr
    NStr=cstr(zNum)
    For i=0 To 3
        zimg(i)=cint(mid(NStr,i+1,1))
    Next
    Dim Pos
    Set Ados=Server.CreateObject("Adodb.Stream")
    Ados.Mode=3
    Ados.Type=1
    Ados.Open
    Set Ados1=Server.CreateObject("Adodb.Stream")
    Ados1.Mode=3
    Ados1.Type=1
    Ados1.Open
    Ados.LoadFromFile(Server.mappath("image_code_body.Fix"))
    Ados1.write Ados.read(1280)
    For i=0 To 3
        Ados.Position=(9-zimg(i))*320
        Ados1.Position=i*320
        Ados1.write ados.read(320)
    Next   
    Ados.LoadFromFile(Server.mappath("image_code_head.Fix"))
    Pos=lenb(Ados.read())
    Ados.Position=Pos
    For i=0 To 9 Step 1
        For j=0 To 3
            Ados1.Position=i*32+j*320
            Ados.Position=Pos+30*j+i*120
            Ados.write ados1.read(30)
        Next
    Next
    Response.ContentType = "image/BMP"
    Ados.Position=0
    Response.BinaryWrite Ados.read()
    Ados.Close:set Ados=nothing
    Ados1.Close:set Ados1=nothing
    If Err Then Session("image_check") = 9999
End Function