How do I turn off the same person to play my RPG game as two different people?
Looking behind the question:
Why do you want the same person to register and play twice?
What advantage would they have if they did?
If there is no (or only minimal) benefit, do not waste time and effort trying to solve the problem without problems. Also, creating obstacles to things will make some people more determined to break or get around them. This can make your problem even worse.
If there is an advantage, you need to think of other, more creative solutions to this problem.
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You can not. It is not possible to uniquely identify users over the Internet. Don't use ip addresses because there might be many people using the same ip, or people using dynamic IPs.
Even if you somehow forced them to give you legal identification, you still won't be absolutely sure that they weren't registered on the site twice as two different accounts.
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I would check the user's IP address every time you enter the game and then log users who come from the same IP and how much they interact. You may find that you have users from the same IP address (i.e. Rooms, spouses who play together and are not actually the same person). You can simply specify these users and control their interactions - for example, is there a chat service in the game? If they never speak to each other, they are most likely the same people and treat them on an individual basis.
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If it's in a web browser, you can bring information like OS or browser, but it doesn't even save, but still safer. It will take the hackers a little more time and you need to look for the possibility that some people might be playing on systems with the same OS and browser.
The safest thing is that people on the same IP phone cannot do anything with each other, like trading or like in a PKR (poker game) game, that you cannot sit at the same table.
Another thing would be smart to do is to use captcha, its a very unfriendly user, but it keeps a lot of bots out
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If it is a browser game, Flash cookies are a relatively stable way of identifying a computer. Or let them pay the minimum amount and identify them by their credit card number - so it will be difficult to make multiple accounts (friends and family cards), but difficult to make many. Depending on your target demographics, it can prevent potential players from registering.
The best approach probably doesn't cause a lot of anxiety and tweak the game balance in such a way that progress is proportional to the time spent playing the game (and use a strong captcha to remove bots). Thus, there will be no benefit to using multiple accounts.
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There are too many ways to get around any of the single player restrictions. FAR is too much.
If the extra player isn't causing any problem, it's not worth the try. You will spend most of your time chasing ghosts instead of focusing on improving the game and making more money.
IP bans do not work, nor do they run cookies as a control mechanism.
Browser fingerprint also doesn't work. People can easily use a second browser.
Even UUIDs won't work as they can be spoofed too.
And if you did manage to find and implement a working method, the user can just use a second computer or laptop, and then what?
People can also isolate the browser to use the same browser twice, thereby defeating browser identification.
And then there are virtual machines ....
We have a huge number of control freaks who want to control every aspect of computing. And the losers are the people who do the calculations.
Every tracking issue I've ever had can be easily bypassed. Be it UUIDs, MAC addresses, IP addresses, fingerprints, etc. And this is also very easy to do.
The best suggestion is to simply monitor for any TOU violations and address the issue accordingly.
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