If you want to use these images: Go ahead. I've placed most of them in the public domain. However >>> While most of them are public domain, a few aren't. Be sure to read the license under each of the enlarged pictures. If you have any questions, please ask.
If you need a hi-res version: I am slowly going back into the archives and making hi-res versions available for a small fee. The photos with such a version already will have a link on their detail page. If you need a hi-res file for a photo that doesn't have one yet, please let me know and I'll try to upload one. Details on the contact page.
About PD Photo:
PDPhoto.org is a repository for free public domain photos. Unless something is clearly marked as being copyrighted, you can assume it is free to use. But if you intend to use an image you find here for commercial use, please be aware that standards for such use are higher. Specifically, you should assume no model release was obtained. And pictures featuring products or property should be used with care. The photos are here to be used, but I don't want you to get either of us in trouble over it.
Swiss Re Building
Conservatory of Flowers in San Francisco
If You Use A Photo:
If you do use one of the picture you find here, please consider supporting the site by linking back and/or giving credit for any pictures you used. But you don't have to. Feel free to leave a message in the comment area for the image you're using if it's something you can link to. The pictures are free for you to use and you should feel good about doing so.