The best option is to download a RAI/XRB wallet to your computer and install it from here http://www.raiblocks.com/#/wallet . after that open the wallet and you will found an address that can be used for captcha job. Also, you can create more account/address if you need and you can make a team of captcha worker.

Now there is no active group that provides captcha job.so try to make your own team and collect mrai and hold them until next pump. don't join any group that is not trusted, may be they can be scammed with you.