I understand how to work with GreaseMonkey I've made several scripts for a private torrent tracker I frequent. You can't make AJAX calls outside of the domain you're working within. If BHW had a captcha, and as you suggest you restrict the script to no particular site, the script is still running on BHW, not recaptcha.org. You can't make a request to download that captcha image from BHW's domain, it's restricted by SOP.thats not true -GM_xmlHttpRequest can reuqst APIs which most captchas services have - a simple REST Webservice
and you can include scripts with the * pattern what then would work on every site...
Edit:
captchamonster works great but has not good plans and no paypal support.