Where to find copyright free photos??

I've been looking around today and I just can't work out where to find a source of free to use photos or pictures that are copyright free that I could use for the web site. It's so frustrating as the internet is full of dog photos and I'm not sure which ones I can use. I don't want to use any without the correct permission.

I guess in time I should be able to get photos of most breeds by contacting individual dog web sites but thats going to take me weeks, if not months.