mmedia - A form 1099 should be issued by the Microstock site (IN this case) to those who provide images and have received a payout during a tax year. The Form 1099 is required to be issued by January 31 for the tax year (Preceeding 12 months - Jan through Dec.) The 1099 is what you would use to record your income (Receipts from MS Sites) on Form 1040, Schedule-C (Business Income and Expenses of an Individual).
If you are not an American citizen, you may not receive one. However if you are required to file an Income Tax return in the U.S. (Form 1040), you will get a Foreign Tax Credit for the amount of tax you paid to a Foreign Country.
I do not want to get into the complex Income Tax Laws of the U.S.; so hope this is sufficient.
I had a similar problem figuring out what thee VAT is. Since I am a U.S. citizen, I am not subject to the VAT tax yet. I say yet, because Americans never know when they will loose their soverignty completely due to the underpinnings of the U.N.
Not too far in the distant future, I suspect that the European Union will dictate to the U.S. Just when that day will come I cannot say, but it will come.