Captcha solving websites pay it's members for helping spam bots to enter into a website. Users working as captcha resolvers are actually entering captcha info on behalf of spam bots.
Some websites claim that they are using this captcha solving jobs for some kind of testing purposes. It's really ridiculous to hear that. Even for a live system a captcha can easily be disabled for any kind of testing purposes. So it is nothing but helping spam bots.
If you are into a captcha / recaptcha solving job then you are working for spammers. You are then being a cheaply paid robot for spam bots.