I'm new here, well - I registered a week ago and yes.. I've experienced this problem too. I think it happens if you attempt to answer a thread before logging in. Whenever I've done that I get the message asking to verify I'm a human but the image doesn't appear below or anywhere else on the page.
After that happens the only way I've found to make it work is to log out and log back in again so lesson learned now. I'm not sure if its an issue with the board or some settings on my computer but as long as there is a work around no problem although I guess it would be nice to resolve the issue to avoid frustrating new users.