A commenter recently complained that the capchas, the images that you have to type in when posting a comment in order to show that you are a person and not a program, are too difficult—a problem I have seen elsewhere online. The obvious problem with not having them is that it makes spam comments easier, since they can be done wholesale by software instead of one at a time by a human being.
As an experiment, I turned off the capcha requirement, with mixed results. Judged by the comments sent in—I have blogger set up to email me copies of all comments—spam increased considerably. Judged by the comments that actually appeared, it didn't. Blogger did a sufficiently good job of filtering out spam so that most of the additional ones got eliminated.
There is still a cost, however—if I want to keep track of comments, including comments on old posts, by reading the emailed copies, I have to wade through a lot of spam. And one reason to keep track of them is that blogger sometimes makes mistakes, in both directions. If I never read the posts that it thinks are spam, some real posts get eliminated.
Suggestions welcome—for the moment I'm leaving capchas off.