If a captcha is capable of warding off spambots, but allows users to easily pass through, this considerably reduces the amount of administration needed for the website. Site operators, who offer user-generated content, won’t need to manually verify posts. In addition, the server will be significantly disburdened when automatic inputs and queries are already blocked before the system’s resource-intensive reactions come into play. But what makes a good captcha?
AI research is making steady progress. Specialized programs are becoming better at reading distorted texts and solving logical problems. In 2014, a Google research team published a concept, with which 99.8% of classic reCAPTCHAs could be automatically solved. The database used 10 million annotated house numbers generated via Google Street View.
Many captcha providers are trying to compensate for advancements in machine learning by making the tests even more difficult. In practice, however, captchas end up being unsolvable.
In 2010, researchers at Stanford University revealed that many captchas present a big challenge for human internet users. In a study, more than 1,100 people were asked to solve more than 318,000 captchas from the most common schemata at the time.
On average, the test subjects completed the graphic captchas in 9.8 seconds. For audio captchas, the subjects needed more than three times as much time, taking 28.4 seconds on average. When the same graphic captcha was shown to three different people, they only came to the same conclusion in 71% of cases. With audio captchas, this number was down to 31%. In addition, the researchers recorded a bounce rate of 50% for audio-based captchas. Whether Human Verification is used and how this is implemented, affects how the visitor sees the website and how much they decide to interact with it.
In 2009, the SaaS company, MOZ, published a blog article on how much captchas affect conversion rates of web forms. In a case study, YouMoz author, Casey Henry, examined more than 50 different company websites over a period of 6 months and concluded that the conversion rates of online forms (e.g. in regards to newsletter subscription) fell by an average of 3.2% when captchas were activated. However, spam was reduced by 88%.
In particular, companies that generate their income from user interactions on their site should consider whether a bounce rate this high is acceptable. The costs of alternative anti-spam methods need to be offset with the income lost from captchas being used.