ProTypers is a very popular captcha job, however you need a special invitation code in order to join, and here it is:
- Please go to http://www.protypers.com/?id=DNUR and click on the button that says “Free Signup!“.
- Fill out your personal details and then enter the code DNUR in the field where it says “Invitation Code“:
This website is very strict when it comes to what email address you can use when signing up, and you may have to try different alternatives. For us a gmail account worked well.