OP suggests to change your user agent to that used by Google to crawl
websites.

Some websites give googlebot more permissions than regular users and don't ask
for captcha.

Not a very reliable method but worth a try.
For a while YouTube did not require JavaScript when you used an outdated
FireFox user agent.

But I think for captchas and javascript you need a tool that is more web 2.0
oriented than httrack :(