http://openclipart.org/

Uses only legal images

If you want to include images from other sources you will need something that is scalable (vector graphics) and you need it to be legal. You just can not take pictures that are not yours an publish them as if they where yours. And no "being in the internet" does not mean it is free for all if you import from http://openclipart.org/ as seen in the file menu you ensure you use images that are licenced on the public domain.