My first check would be images.google.com. You can advance search for high resolution images.
Royalty free just means you don't have to pay every time the image is used/shown. So some image website may claim royalty free but still charge a one time fee.
Not all the images in google searches are royalty free though, am I mistaken? Just because something is published and google provides it in its result does not mean it's available for public use...
Having said that, he can contact the origin of the pics and ask if they can be reused... it'd not hurt to ask...
User-agent: Googlebot-Image
Disallow: /
So Google covers their butt by stating that images may be subject to copyright but what else would Google Images be used for? So I suppose that if you use images from Google images you'll be covered as long as you state each source of the images. Sort of like a list of references in a book to ward off any thoughts of plagiarisim.
I can't imagine someone got sued because of one image, unless it was a company trademark or logo.
I'm certainly not disagreeing with you though. Photos could still very well be copyrighted. I was just making a statement that if photographers/businesses that are wanting to protect their material their are more ways to go about it.
As Ron has stated, commons.wikimedia.org is a very nice site if you want to steer clear of any possibility of copyright issues. It generally states the licensing of each image.
Since you are looking for that many images.. you may want to consider a site that will let you sign up for unlimited image downloads for a set period of time.
This might save you enough time to make the cost worth it.. just a thought