I'm not so sure there are that many limits on algo trading worldwide. Most markets are electronic so how would one even know whether it is algo or human order? And again, what difference does it make where are these located? You could be based in EU and open account with US broker/FCM. You pay EU taxes on profits not US. You could be sending orders from EU or rent US based serves. The company setup in EU could be US company's subsidiary. Therefore I don't see why it would make any difference but maybe I'm missing something.
When you place and pull hundreds of orders a second it's probably a good bet that trader isn't a human!
Well, speaking about futures exchanges, automated trading systems must be registered with the exchange and the orders those systems submit to the exchange are specially tagged (designated) by the exchange. So futures exchanges themselves are completely aware of what is and what is not human. The regulated futures exchanges have determined that it is very much in their interests to monitor and protect their ECN's. They are also not going to allow trading systems that use a disparate level of messaging bandwidth as compared to the filled orders they generate.