GDI+ Security String image

The Code: verify.aspx

	
<%@ Import Namespace="System.Drawing" %>
<%@ Import Namespace="System.Drawing.Imaging" %>
<%@ Import namespace="System.Drawing.Drawing2D" %>
<script language="VB" runat="server">
Sub Page_Load(sender as Object, e as EventArgs)
Dim r as New Random
Dim baseMap as Bitmap = new Bitmap(200, 50)
Dim myGraphic as Graphics = Graphics.FromImage(baseMap)
Dim HBrush As HatchBrush = New HatchBrush( RandomHatch(), GetRandomColor(r))
Dim upBrush as SolidBrush = new SolidBrush(GetRandomColor(r))
Dim fontTitle as Font = new Font("tahoma", 24)
myGraphic.FillRectangle(HBrush, 0, 0, 200, 50)  


myGraphic.DrawString(RandomStringGenerator(6), fontTitle, upBrush, r.Next(0, 80), r.Next(0, 10))
Response.ContentType = "image/jpeg"
baseMap.Save(Response.OutputStream, ImageFormat.JPEG)
myGraphic.Dispose()
baseMap.Dispose()
End Sub

Public Function RandomStringGenerator(ByVal intLen As Integer) As String
    Dim rRandom As New Random()
    Dim Zero As Integer = Asc("0")
    Dim Nine As Integer  = Asc("9")
    Dim capA As Integer  = Asc("A")
    Dim capZ As Integer  = Asc("Z")
    Dim litA As Integer  = Asc("a")
    Dim litZ As Integer  = Asc("z")    
    
Dim iRandNum as integer
	Dim strTemp as String = ""
	Dim i As Integer
	While i < intLen
	iRandNum = rRandom.Next(Zero, litZ)
		If ((((iRandNum > = Zero) And (iRandNum <= Nine) Or _
		(iRandNum > = capA) And (iRandNum < = capZ) Or _
		(iRandNum > = litA) And (iRandNum < = litZ)))) Then 
			strTemp = strTemp + Chr(iRandNum) 
			i+=1
	       End If
	End while
	Return strTemp
End Function

Public Function RandomHatch() As HatchStyle 
	Randomize() 
	Select Case Rnd() * 56 
		Case Is < 1 : Return HatchStyle.BackwardDiagonal
		Case Is < 2 : Return HatchStyle.Cross
		Case Is < 3 : Return HatchStyle.DarkDownwardDiagonal
		Case Is < 4 : Return HatchStyle.DarkHorizontal
		Case Is < 5 : Return HatchStyle.DarkUpwardDiagonal
		Case Is < 6 : Return HatchStyle.DarkVertical
		Case Is < 7 : Return HatchStyle.DashedDownwardDiagonal
		Case Is < 8 : Return HatchStyle.DashedHorizontal
		Case Is < 9 : Return HatchStyle.DashedUpwardDiagonal
		Case Is < 10 : Return HatchStyle.DashedVertical
		Case Is < 11 : Return HatchStyle.DiagonalBrick
		Case Is < 12 : Return HatchStyle.DiagonalCross
		Case Is < 13 : Return HatchStyle.Divot
		Case Is < 14 : Return HatchStyle.DottedDiamond
		Case Is < 15 : Return HatchStyle.ForwardDiagonal
		Case Is < 16 : Return HatchStyle.Horizontal
		Case Is < 17 : Return HatchStyle.HorizontalBrick
		Case Is < 18 : Return HatchStyle.LargeCheckerBoard
		Case Is < 19 : Return HatchStyle.LargeConfetti
		Case Is < 20 : Return HatchStyle.LargeGrid
		Case Is < 21 : Return HatchStyle.LightDownwardDiagonal  
		Case Is < 22 : Return HatchStyle.LightHorizontal
		Case Is < 23 : Return HatchStyle.LightUpwardDiagonal
		Case Is < 24 : Return HatchStyle.LightVertical
		Case Is < 25 : Return HatchStyle.DottedGrid
		Case Is < 26 : Return HatchStyle.Max
		Case Is < 27 : Return HatchStyle.Min
		Case Is < 28 : Return HatchStyle.NarrowHorizontal
		Case Is < 29 : Return HatchStyle.NarrowVertical
		Case Is < 30 : Return HatchStyle.OutlinedDiamond
		Case Is < 31 : Return HatchStyle.Percent05
		Case Is < 32 : Return HatchStyle.Percent10
		Case Is < 33 : Return HatchStyle.Percent20
		Case Is < 34 : Return HatchStyle.Percent25
		Case Is < 35 : Return HatchStyle.Percent30
		Case Is < 36 : Return HatchStyle.Percent40
		Case Is < 37 : Return HatchStyle.Percent50
		Case Is < 38 : Return HatchStyle.Percent60
		Case Is < 39 : Return HatchStyle.Percent70
		Case Is < 40 : Return HatchStyle.Percent75
		Case Is < 41 : Return HatchStyle.Percent80
		Case Is < 42 : Return HatchStyle.Percent90
		Case Is < 43 : Return HatchStyle.Plaid
		Case Is < 44 : Return HatchStyle.Shingle
		Case Is < 45 : Return HatchStyle.SmallCheckerBoard
		Case Is < 46 : Return HatchStyle.SmallConfetti
		Case Is < 47 : Return HatchStyle.SmallGrid
		Case Is < 48 : Return HatchStyle.SolidDiamond
		Case Is < 49 : Return HatchStyle.Sphere
		Case Is < 50 : Return HatchStyle.ZigZag
		Case Is < 51 : Return HatchStyle.Trellis
		Case Is < 52 : Return HatchStyle.Vertical
		Case Is < 53 : Return HatchStyle.Wave
		Case Is < 54 : Return HatchStyle.Weave
		Case Is < 55 : Return HatchStyle.WideDownwardDiagonal
		Case Is < 56 : Return HatchStyle.WideUpwardDiagonal
	End Select 
End Function 


Private Function GetRandomColor(r) As Color
    Return Color.FromArgb(r.Next(0, 256), r.Next(0, 256), r.Next(0,256))
End Function
</script>

Usage

<img src="verify.aspx" />

Real Time Example

Comments

kajanth 2/9/2005 2:55:59 AM hi this code is vey neat. i need to develop something similar for my uni project and was wondering if you could give me some tips and how i can use this to block automation bots.

kajan

mkajanth@hotmail.com

Joe Maddalone
2/9/2005 7:08:25 AM Pass strTemp to a public variable. Use a form / input field / submit button. Make sure the value entered in the field matches the strTemp value. DONE.

smith288 3/28/2005 11:40:59 AM The random colors can be hard to see from time to time with weird fore/back combos of blue and black or even black and black.

Joe Maddalone
3/28/2005 11:56:53 AM Repeat this mantra: "That`s a feature, not a bug, a feature." "That`s a feature, not a bug, a feature." "That`s a feature, not a bug, a feature."

Rahul Dev Katarey
6/1/2005 3:37:58 AM its cool, but can do this with simple asp ".asp" ?

Rahul Dev Katarey
6/1/2005 3:39:15 AM its cool, but can do this with simple asp ".asp" ? i Just Want to know

Terry 6/3/2005 9:42:05 AM Joe: I placed an image Webcontrol on a form. How would you save your image to an existing image or placeholder. Thanks

Joe Maddalone
6/4/2005 2:01:19 PM Terry, sounds simple enough... I am sure when I get the chance to look into your question it should not be too hard.

David 10/31/2007 1:38:36 AM Hi joe Can i show this image in an image control?

Joe Maddalone 11/4/2007 10:38:48 PM I dont see why not.

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