From previous experience, it would take a matter of a few hours for them to adjust.
so freebitco.in ever used the user's balance as a captcha ?
No, but it would be trivial to automate. When we've made other changes to the captcha implementation it only takes a few hours for them to notice and recode.
I just think that maybe those who use captcha solver services will not be as easy as now because the user balance is added as a checksum
a few days ago I tried on sites that use captcha that are supported and it is very easy, we just enter some kind of token code from captcha solver as an API and captcha is finished quite quickly
so if you add a user balance as a checksum I think it will be difficult for captcha solver services because they have to make adjustments to captcha workers as well.
I think it will be complicated for them because they have to make a new type of captcha service.