If you make profits you should declare them like any other person. You'll be taxed as a trader, more specifically a FOREX trader, as you are trading with currencies.
That's not always true. In the US, for example, Bitcoin is not a currency, but it's treated like property. Therefore, you pay long term capital gains if you have held BTC for more than 1 year. Also, in the US capital gain depends on your income, which is why, for example, Steve Jobs had a salary of $1 as CEO of Apple.