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 webbots 2/17/2019 ITS102-12, Third Class

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? 2/17/2019 ITS102-12, Third Class

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! 2/17/2019 ITS102-12, Third Class

CAPTCHA Completely Automated Public Turing test to tell Computers and Humans Apart 2/17/2019 ITS102-12, Third Class

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 CAPTCHA 2/17/2019 ITS102-12, Third Class

How Computers Read Optical 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. 2/17/2019 ITS102-12, Third Class

Frustrating OCR 1 Use messy background. 2 Separate background from print Use messy background. 2 Pick up individual characters Have them blend with each other. 3 Find strokes, loops, etc Make the letters “wiggly” 4 Apply classification rules It should be hopeless by this point. 2/17/2019 ITS102-12, Third Class

Make your own CAPTCHA www.codeproject.com/KB/aspnet/ CaptchaImage.aspx 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.htm 2/17/2019 ITS102-12, Third Class

From Yahoo’s Briefcase Some Weak CAPTCHAs From Paypal From Yahoo’s Briefcase 2/17/2019 ITS102-12, Third Class

Some CAPTCHAs that may be too hard for people From Yahoo: From Passport: 2/17/2019 ITS102-12, Third Class

But Human Vision is Amazing 2/17/2019 ITS102-12, Third Class

But Human Vision is Amazing 2/17/2019 ITS102-12, Third Class

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. 2/17/2019 ITS102-12, Third Class

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 K 2/17/2019 ITS102-12, Third Class