Web sites that accept postings from the public, like this wiki, are often abused by spammers who use automated tools to post their links to many sites. While these spam links can be removed, they are a significant nuisance.
Sometimes the OpenStreetMap wiki may ask you to solve a little mathematical puzzle. This will allow real humans to make their posts while putting off most spammers and other robotic attackers. The maths puzzle is shown when you first create a wiki account, and when you are adding new external links to a page.
Please contact the sysadmins for assistance if this is unexpectedly preventing you from making legitimate posts.
Hit the 'back' button in your browser to return to the page editor.