Editing Transaction costs/Brainstorming (section)

=== CAPTCHAs ===

CAPTCHAs are an common transaction cost associated with contributing to wikis, forums, or blog comments. They come in a variety of forms. The most common is an image-based CAPTCHA where contributors are asked to decode an image of distorted text. CAPTHCAs are very simple "Turing Tests" which are designed to allow a piece of computer software to distinguish between a human user and a script. They exist to block automated spam of wikis, websites that allow contents, and other forms of user generated content.

General thoughts:

* CAPTCHAs provide a simple cost that will, given a particular CAPTCHA, be roughly equivalent.
* CAPTCHAs do not present a cost that is equal to all users (e.g., blind people find CAPTCHAs completely impossible since they cannot see the images).
* My sense is that CAPTCHAs more difficult is likely to increase the likelihood that a user will fail the CAPTCHA but unlikely to make it take much more time. 
* CAPTCHAs, at least as they are frequently employed, provide a post-facto cost to most users. Users will usually invest in their comment or wiki page before they even consider the CAPTCHA or know that they are installed.
* A user could be asked to solve a series of CAPTCHAs or could fail one CAPTCHA (intentionally) or be given an ambiguous CAPTCHA and asked to solve more. This could happen before a contribution. Many users might give up and decide that it was not worth the contribution. However, if CAPTCHAs were obviously impossible, users might become frusterated. If CAPTCHAs were not ambiguous enough, users might assume the system was broken for not accepting known correct answers and give up for that
* Use of such a comment in blog comments would be tricky because people may be more or less likely to comment on a particular article or issue if it is more interesting. If use on blogs were to be done, it would have to done on a large sample of different blogs over a period of time and would not be connected to a the work of particular posts or particular authors. Using it multiple times on a single article seems suspect because a single blog post is unlikely to get a very large number of comments.