I tried to solve the HN captcha. It's almost impossible and you have to get really lucky that you get an easy image. The audio alternative is pretty messed up too.
are you using TOR or any other IP masking solution?
The more reCaptchas get solved or requested by a particular IP the harder they become, so if you are behind a IP that has been used for solving/requesting a lot of reCaptchas it is close to impossible to get a readable one (took me about 80 tries till I got one right when I used TOR). I don't know what exactly determines this difficulty but it is definitely there and Google talks about it here: http://googleonlinesecurity.blogspot.de/2013/10/recaptcha-ju...