Here are four sites to search for photos (and clipart) for your ebook covers or your blog.
1. Photoshop Support . Here you'll find a large list of stock photo sites. Some charge a fee but, if you read the descriptions below the list, you'll find some sites are royalty free (but read all copyright information).
2. imcphoto.net . A small site, but the photos are excellent and free. Scroll down until you see the photos and it says Public Domain Photos.
3. PD Photo.org . This site has hundreds of free and public domain photos. Search the Category Column on the right.
4. WP Clipart. Not a public domain photo site, this is a free clipart site. (The thumbnails don't do the clipart justice. Click on the thumbnail to see what the clipart really looks like.)
To test these sites, I've downloaded from each. They were easy and simple to use.
If you've used any other photo download sites, post them in the Comment section below.
Usual disclaimer: When going to unfamiliar sites, keep your virus scanner on and firewall up.