I agree it is unfair that you have to pay taxes twice, but unfortunately this is the rule in some countries, unless they have the reciprocity agreement.

I have a bank account in UK and, after filling in a certain form for non-residents, I am free of taxes on the investments earnings.  It is basically an incentive to have money in UK, as I understand.  And the logic behind it is that I take no advantage of any benefits from the tax collected, as I don't live in UK.  That's the same logic in VAT return.

Here in Brazil income taxes vary with the amount of earnings.  I don't remember the ranges, but I am in the 27% range.  I don't know how to call this, I don't pay 27% of my income, it's rather 27% over a certain amount that is tax exempted, so it's like 0.27*(X-Y), X being the gross income and Y being the exempt income.  Anyway, as I am in the 27% range, any extra income (such as stock photography earnings) means paying 27% of taxes.  This is awful, as in the end our public services normally lack quality, but this is another story.

Regards,
Adelaide

Because it's the law? 

 masive chains of gas stations, or supermarkets are not paying taxes entirely, nobody pay taxes with big companies, and I, a small man should pay? no way.... when those tycoons that earn 1 million euros per month start paying taxes, so will I.