PublicDomainPictures.net is a repository for free public domain images. Free for private and commercial use.

There a large catalogue of images here in multiple categories. The images are of varying quality but for the price are great. There is also a Background category and an Illustrations category. Without looking through all of the images this website is an excellent resource for public domain images.

Clicking on a photo will provide you with detailed information about the camera used, the artist, license, and several other technical features. The images are also easy to search because the images are all tagged.