Remark: This is not an official tax advise and I am not responsible for any misunderstanding. I simply share what I learned from my accountant and what works for me.
Stock photography falls under simplified light taxation that applies to art/copyright works.
That means you don't need to register a business (even self-employed is not necessary), you can declare the income as your personal.
The tax applied is 15%
You are allowed to declare 50% of your overall stock income as your cost, so 15% is taken from half of your income (up to the ceiling of 13,840 Eur for income 2009 - and you can declare 25% of income as cost for the second 13,840 Eur).
On a practical side - if you are filling paper tax declaration you need to request tax office to provide you the second part (that is usually used by business); if you are filling your tax online in tax-on-web you can enter data directly.
You declare your total income per year in Euro in field 1190; and half of the a mount as cost in field 1191 (if your annual income is <13,840 Eur).
How to count the amount: Typically you don't receive any supporting documents from stock agencies (unless it's a German one). So just write down yourself every dollar amount that you transferred during reporting year from stock sites to your paypal account (or to your bank account or whatever method you used); and convert every transaction to Euro using historical exchange rate on that date (find in internet). Of course you keep Euro amount if you are receiving money from European agency. Then sum all Euro amounts and use it your for declaration. Attach your calculation to your declaration.
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