Recaptcha required to join a community

[daluci]

Title
Recaptcha required to join a community

Short, concise description of the idea
Require users trying to join a community to pass a spambot challenge.

Full description of the idea
There's been a recent spurt of spammy/malware-linking videos showing up in communities I watch on my friendspage. Most of these spam journals are members of more than a thousand communities, and just post their videos all over the place.

I think it would be helpful if a user had to pass a spambot challenge when joining a community with open membership. Since the challenge has to be passed in order to create an account initially, this shouldn't keep users from joining, but it may lower the number of bots joining open communities.

I know that community moderators taking more time and moderating people who join or the posts that are submitted can keep this kind of content away, but a lot of the communities that have the problem don't have a moderator that pays attention, and the subject material just isn't popular enough to justify making /another/ community and trying to get everyone to relocate.
An ordered list of benefits

• Lower the number of malicious posts to communities with open membership
• Make it harder for people to spam communities

An ordered list of problems/issues involved

• Could be annoying for actual users
• Difficult to code?
• I'm not sure when in the process this could appear
• Could be avoided by having more active moderators of communities
• Can pose an accessibility problem to users who have difficulty answering reCAPTCHA challenges.