It’s CAPTCHA for a reason – Why you can’t OCR CAPTCHA

by Ilya Evdokimov | Dec 10, 2009 | OCR

I’ve been surprised recently about the number of project requests and Twitter conversation’s insisting that OCR can be used to read CAPTCHA. A CAPTCHA is that crazy set of letters and numbers most websites ask you to enter when completing a web form. The purpose of a CAPTCHA is to prevent web bots to create accounts on websites for use in spamming or other malicious activities. It’s surprising the number of organizations both private and public that want people to solve this problem of reading CAPTCHA for them. Most all of these companies ask for the use of OCR technology to do so.

I’m sorry, but the answer is it’s not possible with OCR. The reason it’s not possible is because CAPTCAH is not an OCR problem. It would be more logical to call it ICR ( Hand Print ), but this is still a stretch. OCR is Optical Character Recognition which is reading of typographic text. CAPTCHA fonts are clearly not typographic. To be typographic they would have to have the same baseline (bottom border), same font height for each character in the same class, etc. CAPTCHA fonts resemble more closely hand-print which is ICR processing. However even ICR technology is expecting some consistency, for the most part in a given day and time you will write the word “CVision” pretty much the same across a form. This allows ICR to understand subject hand strokes etc. in creating the character. This level of consistency is simply not present in CAPTCHA’s. CAPTCHA’s deploy backgrounds and ever moving lines to prevent the consistency of even their already bizarre fonts. For the most part each CAPTCHA system at any given moment in time will produce a different character variation for each character possible.

While the idea of processing CAPTCHA’s is technically enticing, actually wanting to do it has obvious malicious intent. Conversion of CAPTCHA’s would require a combination of varying recognition technologies, adaptive pattern training, and imaging techniques. I’m not convinced that the effort in creating such an approach is fiscally feasible, especially when the average project is offering fifteen dollars to complete it. My job today is to set the record straight and let the world know that CAPTCHA processing is not a job for OCR and ICR technology period.

Chris Riley – Sr. Solutions Architect