asp图片验证码
调用：
<img src="inc/checkcode.asp">

验证码：
checkcode.asp
<%
Option Explicit ' 显示声明
Class Com_GifCode_Class
'''''''''''''''''''''''''''''''''''''''''''''
' Author: Layen 84815733(QQ)
' Thanks: Laomi, Laomiao, NetRube
' 2006-01-02
'''''''''''''''''''''''''''''''''''''''''''''
Public Noisy, Count, Width, Height, Angle, Offset, Border

Private Graph(), Margin(3)

Private Sub Class_Initialize()
Randomize
Noisy = 6 ' 干扰点出现的概率
Count = 4 ' 字符数量
Width = 80 ' 图片宽度
Height = 20 ' 图片高度
Angle = 2 ' 角度随机变化量
Offset = 20 ' 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.cachecontrol="no-cache"      '如果去掉此句则后退不刷新验证码
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("GetCode") = mCode.Create()
mCode.Output()
Set mCode = Nothing
%>