In 2010 the University of California at San Diego conducted a large scale study of those CAPTCHA's farms and found out that the retail price for solving one million CAPTCHAs is as low as $1,000. Another technique used consists of using a script to re-post the target site's CAPTCHA as a CAPTCHA to a site owned by the attacker, which unsuspecting humans visit and correctly solve within a short while for the script to use. However, there is controversy around the economic viability of such an attack. There are multiple Internet companies like 2Captcha and DeathByCaptcha that offer human and machine backed CAPTCHA solving services for as low as US$0.50 per 1000 solved CAPTCHAs. These services offer APIs and libraries that enable users to integrate CAPTCHA circumvention into the tools that CAPTCHAs were designed to block in the first place. Howard Yeend has identified two implementation issues with poorly designed CAPTCHA systems:  Sometimes, if part of the software generating the CAPTCHA is client-side (the validation is done on a server but the text that the user is required to identify is rendered on the client side), then users can modify the client to display the un-rendered text. Some CAPTCHA systems use MD5 hashes stored client-side, which may leave the CAPTCHA vulnerable to a brute-force attack. Some notable attacks against various CAPTCHAs schemas include:  With the demonstration that text distortion based  CAPTCHAs are vulnerable to machine learning based attacks, some researchers have proposed alternatives including image recognition CAPTCHAs which require users to identify simple objects in the images presented. The argument in favor of these schemes is that tasks like object recognition are typically more complex to perform than text recognition and therefore should be more resilient to machine learning based attacks. Here are some of notable alternative CAPTCHA schemas: