Fighting the WebBots• A webbot is a program that visits web  sites for all kinds of purposes.• For example, Google webbots...
Webbots and Spam• Spammers send webbots to get e-mail  accounts from sites that offer them for  free.• How can you tell th...
Are you a person or a bot?• We know that there are certain things  that computers cannot do.• Ask the “applicant” to do so...
CAPTCHA• Completely    Automated    Public    Turing test to tell    Computers and    Humans    Apart6/7/2011           IT...
CAPTCHA• CAPTCHA does not have to be text, but  “computer unreadable” text is  convenient.• Alternatives include pictures....
How Computers ReadOptical Character Recognition (OCR)• Step 1: Separate print (usually dark) from  background (usually lig...
Frustrating OCR           Separate     1     background          Use messy background.           from print           Pick...
Make your own CAPTCHA• A web site that offers you the means:• www.codeproject.com/KB/aspnet/  CaptchaImage.aspx• For a gen...
Some Weak CAPTCHAs      From Paypal       From Yahoo’s         Briefcase6/7/2011              ITS102-12, Third Class   9
Some CAPTCHAs that may be       too hard for people     From Yahoo:   From Passport:6/7/2011            ITS102-12, Third C...
But Human Vision is Amazing6/7/2011   ITS102-12, Third Class   11
But Human Vision is Amazing6/7/2011   ITS102-12, Third Class   12
Non Text CAPTCHAs• Use pictures as CAPTCHAs• Plus: There are very tough to break• Minus:     – Need to label a huge number...
Synthetic Pictures           (an idea by M. Kaplan)                          Please click on or enter each                ...
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WebBots

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WebBots

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WebBots

  1. 1. Fighting the WebBots• A webbot is a program that visits web sites for all kinds of purposes.• For example, Google webbots make copies of all web sites for their search engines.• The challenge is to stop malicious webbots6/7/2011 ITS102-12, Third Class 1
  2. 2. Webbots and Spam• Spammers send webbots to get e-mail accounts from sites that offer them for free.• How can you tell that someone who asks for an e-mail account is a person or a webbot?6/7/2011 ITS102-12, Third Class 2
  3. 3. Are you a person or a bot?• We know that there are certain things that computers cannot do.• Ask the “applicant” to do something that computers cannot do.• Cook a meal?• Read something impossible for computers to read!6/7/2011 ITS102-12, Third Class 3
  4. 4. CAPTCHA• Completely Automated Public Turing test to tell Computers and Humans Apart6/7/2011 ITS102-12, Third Class 4
  5. 5. CAPTCHA• CAPTCHA does not have to be text, but “computer unreadable” text is convenient.• Alternatives include pictures.• For example, ask if a person in a pictures is smiling or not. What is wrong with such a CAPTCHA6/7/2011 ITS102-12, Third Class 5
  6. 6. How Computers ReadOptical Character Recognition (OCR)• Step 1: Separate print (usually dark) from background (usually light).• Step 2: Pick up individual characters (group of dark pixels)• Step 3: Identify their shape by looking for strokes, loops, corners, etc• Step 4: Use rules to classify. For example, an H has two vertical strokes and a short horizontal strokes.6/7/2011 ITS102-12, Third Class 6
  7. 7. Frustrating OCR Separate 1 background Use messy background. from print Pick up Have them blend with 2 individual characters each other. Find strokes, 3 loops, etc Make the letters “wiggly” Apply It should be hopeless by 4 classification rules this point.6/7/2011 ITS102-12, Third Class 7
  8. 8. Make your own CAPTCHA• A web site that offers you the means:• www.codeproject.com/KB/aspnet/ CaptchaImage.aspx• For a general tutorial see:• www.theopavlidis.com/technology/ captcha/tutorial.htm6/7/2011 ITS102-12, Third Class 8
  9. 9. Some Weak CAPTCHAs From Paypal From Yahoo’s Briefcase6/7/2011 ITS102-12, Third Class 9
  10. 10. Some CAPTCHAs that may be too hard for people From Yahoo: From Passport:6/7/2011 ITS102-12, Third Class 10
  11. 11. But Human Vision is Amazing6/7/2011 ITS102-12, Third Class 11
  12. 12. But Human Vision is Amazing6/7/2011 ITS102-12, Third Class 12
  13. 13. Non Text CAPTCHAs• Use pictures as CAPTCHAs• Plus: There are very tough to break• Minus: – Need to label a huge number of pictures. – If we use few pictures the webbot can just keep guessing.6/7/2011 ITS102-12, Third Class 13
  14. 14. Synthetic Pictures (an idea by M. Kaplan) Please click on or enter each letter corresponding to the following list in the field below. You must enter them in the exact sequence listed. C K6/7/2011 ITS102-12, Third Class 14

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