Not one for generally being a grammar/spelling nazi or anything... and given that the developer is registered in the Phillipines... I am however a little concerned at the rather poor math/explanation offered on that website...
CaptchaCO.IN is free and will always be free for everyone to use and integrate. However, to keep-up with maintenance like server and other website and staff expenses needed to keep the site and service running 24/7, we will deduct a processing fee of 2% if not 0.001 BTC or which is higher per pay captcha payment transaction.
Which means if someone pays you through your pay captcha installation of 0.01 BTC we take 2% of it which is 0.001 BTC and you keep 0.009 BTC but if your pay captcha installation earns 0.1 BTC we will deduct a fee of 0.002 BTC which is 2% of the whole transaction.
Firstly, taking a fee means that it isn't free...
Secondly, last time I checked... 2% of 0.01 is NOT 0.001... 0.001 would be 10%. I suspect that in the very confusing bolded part of their message that they meant to say: "We will deduct a processing fee of 0.001 BTC or 2% of the transaction amount, whichever is higher."
Also, as someone else pointed out, there isn't any sort of explanation into how the wallet works, where the funds are stored, who holds the keys etc... and the wallet seems to just be a side business on them providing a paywall service for your website.
Would have to recommend staying away from this one.