为了防止机械式的破解或者提交，验证码起到了关键的作用，现在基本上对于登录，或者论坛的回复等等很多的应用都用到了验证码
验证码文件如下：
代码
<%
Option Explicit ' 显示声明
Class Com_GifCode_Class
Option Explicit ' 显示声明
Class Com_GifCode_Class
Public Noisy, Count, Width, Height, Angle, Offset, Length, Border
Private Graph(), Margin(3)
Private Sub Class_Initialize()
Randomize
Noisy = 4 ' 干扰点出现的概率
Count = 3 ' 字符数量
Width = 60 ' 图片宽度
Height = 22 ' 图片高度
Angle = 1 ' 角度随机变化量
Offset = 2 ' 偏移随机变化量
Border = 1 ' 边框大小
End Sub
Public Function Create()
Const cCharSet = "123456789"
Dim i, x, y
Dim vValidCode : vValidCode = ""
Dim vIndex
ReDim Graph(Width-1, Height-1)
For i = 0 To Count - 1
vIndex = Int(Rnd * Len(cCharSet))
vValidCode = vValidCode + Mid(cCharSet, vIndex+1 , 1)
SetDraw vIndex, i
Next
Create = vValidCode
End Function
Sub SetDot(pX, pY)
If pX * (Width-pX-1) >= 0 And pY * (Height-pY-1) >= 0 Then
Graph(pX, pY) = 1
End If
End Sub
Public Sub SetDraw(pIndex, pNumber)
' 字符数据
Dim DotData(8)
DotData(0) = Array(30, 15, 50, 1, 50, 100)
DotData(1) = Array(1 ,34 ,30 ,1 ,71, 1, 100, 34, 1, 100, 93, 100, 100, 86)
DotData(2) = Array(1, 1, 100, 1, 42, 42, 100, 70, 50, 100, 1, 70)
DotData(3) = Array(100, 73, 6, 73, 75, 6, 75, 100)
DotData(4) = Array(100, 1, 1, 1, 1, 50, 50, 35, 100, 55, 100, 80, 50, 100, 1, 95)
DotData(5) = Array(100, 20, 70, 1, 20, 1, 1, 30, 1, 80, 30, 100, 70, 100, 100, 80, 100, 60, 70, 50, 30, 50, 1, 60)
DotData(6) = Array(6, 26, 6, 6, 100, 6, 53, 100)
DotData(7) = Array(100, 30, 100, 20, 70, 1, 30, 1, 1, 20, 1, 30, 100, 70, 100, 80, 70, 100, 30, 100, 1, 80, 1, 70, 100, 30)
DotData(8) = Array(1, 80, 30, 100, 80, 100, 100, 70, 100, 20, 70, 1, 30, 1, 1, 20, 1, 40, 30, 50, 70, 50, 100, 40)
Dim vExtent : vExtent = Width / Count
Margin(0) = Border + vExtent * (Rnd * Offset) / 100 + Margin(1)
Margin(1) = vExtent * (pNumber + 1) - Border - vExtent * (Rnd * Offset) / 100
Margin(2) = Border + Height * (Rnd * Offset) / 100
Margin(3) = Height - Border - Height * (Rnd * Offset) / 100
Dim vStartX, vEndX, vStartY, vEndY
Dim vWidth, vHeight, vDX, vDY, vDeltaT
Dim vAngle, vLength
vWidth = Int(Margin(1) - Margin(0))
vHeight = Int(Margin(3) - Margin(2))
' 起始坐标
vStartX = Int((DotData(pIndex)(0)-1) * vWidth / 100)
vStartY = Int((DotData(pIndex)(1)-1) * vHeight / 100)
Dim i, j
For i = 1 To UBound(DotData(pIndex), 1)/2
If DotData(pIndex)(2*i-2) <> 0 And DotData(pIndex)(2*i) <> 0 Then
' 终点坐标
vEndX = (DotData(pIndex)(2*i)-1) * vWidth / 100
vEndY = (DotData(pIndex)(2*i+1)-1) * vHeight / 100
' 横向差距
vDX = vEndX - vStartX
' 纵向差距
vDY = vEndY - vStartY
' 倾斜角度
If vDX = 0 Then
vAngle = Sgn(vDY) * 3.14/2
Else
vAngle = Atn(vDY / vDX)
End If
' 两坐标距离
If Sin(vAngle) = 0 Then
vLength = vDX
Else
vLength = vDY / Sin(vAngle)
End If
' 随机转动角度
vAngle = vAngle + (Rnd - 0.5) * 2 * Angle * 3.14 * 2 / 100
vDX = Int(Cos(vAngle) * vLength)
vDY = Int(Sin(vAngle) * vLength)
If Abs(vDX) > Abs(vDY) Then vDeltaT = Abs(vDX) Else vDeltaT = Abs(vDY)
For j = 1 To vDeltaT
SetDot Margin(0) + vStartX + j * vDX / vDeltaT, Margin(2) + vStartY + j * vDY / vDeltaT
Next
vStartX = vStartX + vDX
vStartY = vStartY + vDY
End If
Next
End Sub
Public Sub Output()
Response.Expires = -9999
Response.AddHeader "pragma", "no-cache"
Response.AddHeader "cache-ctrol", "no-cache"
Response.ContentType = "image/gif"
' 文件类型
Response.BinaryWrite ChrB(Asc("G")) & ChrB(Asc("I")) & ChrB(Asc("F"))
' 版本信息
Response.BinaryWrite ChrB(Asc("8")) & ChrB(Asc("9")) & ChrB(Asc("a"))
' 逻辑屏幕宽度
Response.BinaryWrite ChrB(Width Mod 256) & ChrB((Width \ 256) Mod 256)
' 逻辑屏幕高度
Response.BinaryWrite ChrB(Height Mod 256) & ChrB((Height \ 256) Mod 256)
Response.BinaryWrite ChrB(128) & ChrB(0) & ChrB(0)
' 全局颜色列表
Response.BinaryWrite ChrB(255) & ChrB(255) & ChrB(255)
Response.BinaryWrite ChrB(0) & ChrB(85) & ChrB(255)
' 图象标识符
Response.BinaryWrite ChrB(Asc(","))
Response.BinaryWrite ChrB(0) & ChrB(0) & ChrB(0) & ChrB(0)
' 图象宽度
Response.BinaryWrite ChrB(Width Mod 256) & ChrB((Width \ 256) Mod 256)
' 图象高度
Response.BinaryWrite ChrB(Height Mod 256) & ChrB((Height \ 256) Mod 256)
Response.BinaryWrite ChrB(0) & ChrB(7) & ChrB(255)
Dim x, y, i : i = 0
For y = 0 To Height - 1
For x = 0 To Width - 1
If Rnd < Noisy / 100 Then
Response.BinaryWrite ChrB(1-Graph(x, y))
Else
If x * (x-Width) = 0 Or y * (y-Height) = 0 Then
Response.BinaryWrite ChrB(Graph(x, y))
Else
If Graph(x-1, y) = 1 Or Graph(x, y) Or Graph(x, y-1) = 1 Then
Response.BinaryWrite ChrB(1)
Else
Response.BinaryWrite ChrB(0)
End If
End If
End If
If (y * Width + x + 1) Mod 126 = 0 Then
Response.BinaryWrite ChrB(128)
i = i + 1
End If
If (y * Width + x + i + 1) Mod 255 = 0 Then
If (Width*Height - y * Width - x - 1) > 255 Then
Response.BinaryWrite ChrB(255)
Else
Response.BinaryWrite ChrB(Width * Height Mod 255)
End If
End If
Next
Next
Response.BinaryWrite ChrB(128) & ChrB(0) & ChrB(129) & ChrB(0) & ChrB(59)
End Sub
End Class
Dim mCode
Set mCode = New Com_GifCode_Class
Session("getYzm") = mCode.Create()
mCode.Output()
Set mCode = Nothing
%>
将以上代码保存为gif.asp，或者什么名字都可以，使用如下代码来使用：
<input name="yzm" type="text" size="6" /><img src='gif.asp' align='absmiddle' border='0' height="18" />
页面中显示效果：
asp的判断代码如下：
代码
<%
dim yzmStr
yzmStr=Request.Form("yzm")
If Trim(yzmStr)=Empty Or Trim(Session("getYzm"))<>Trim(yzmStr) Then
response.write("<script language=javascript>alert('验证码错误，请重新输入！');history.back()</script>")
response.end
end if
%>
dim yzmStr
yzmStr=Request.Form("yzm")
If Trim(yzmStr)=Empty Or Trim(Session("getYzm"))<>Trim(yzmStr) Then
response.write("<script language=javascript>alert('验证码错误，请重新输入！');history.back()</script>")
response.end
end if
%>