http://www.openclipart.org/

Aspoň to teda tak chápu, že použití klipartů je "volný", tj. mimo jiné zdarma. Usuzuju tak ze stránky http://www.openclipart.org/wiki/FAQ kde je mimo jiné (cituji):
"What limitations are there in how I can use the clipart?

There are no limitations, you can do whatever you wish with it.

We select the Public Domain for the clipart in order to provide maximum flexibility and ease of use to the user. You can put the clipart into your own drawings without any affect on the copyright or license of your work. There are no requirements to include attribution of the clipartist. You can edit and modify the clipart as you wish and redistribute it under your own terms." --- konec citace.

Pokud jsem uvedl nepravdivou info, prosím kompetentní osoby k vyjádření.

Pavel