Finding the correct image for a banner

Hello,

I am thinking of creating a few animated gifs for standard sized banners. I see alot of banners having random people in them, or cars or animals, etc.. anything that will make the banner look more professional and to the point. My question is, how do you get those images? Surely the artist doesn't go around the street snapping photos of people and then transfer them onto to the computer. Is there a database of these pics people can use? How does that work exactly?

Thanks

http://creative.gettyimages.com/source/home/home.aspx

Stock photo website, has a load of stock photos, you have to pay for the rights to most of these ones, but try a search on stock photos and you should find some royalty free photos you can use

http://www.sxc.hu/

Totally free stock exchange site.