All imagery is copyright protected from the moment it is created. Resold or not, if you display someone elses copyright protected images publicly, you can get into trouble.
There's a big difference between "rights managed", "royalty free" and "public domain" imagery. And when I say imagery, it could be photographs, drawings, designs and more.
If you misinterpret these types of imagery and use a protected image, you can face a lawsuit for copyright infringement -
www.copyright.gov
Rights managed basically means the creator is giving you the license to use his artwork for a very specific purpose. He can limit the number of copies produced, how it's displayed and much more. Once you've used the art for that specific purpose, generally, it can not be used again without another agreement.
Royalty free is generally less restrictive than rights managed and the creator allows you to use the imagery within the terms of the license agreement. The main difference from rights managed is you normally can reproduce the design as many times as you want and reproduce it in many formats - print, web, etc.
Public Domain means that any copyright protection afforded to the designer has long expired and the imagery is free to use by anyone and for any purpose. There are other circumstances that can occur that make an image public domain too.
In all circumstances, you need to do your homework and be sure of the source of the artwork. Without doing the background work, you and your client can get screwed.
Anyway, I think the photos you are looking for are "public domain". Generally, you can get these from the archives at your library or online from the federal government, which in most cases, can not hold a copyright. And just an FYI, I've seen public domain photos that you can download (for free) from some federal agency sites on websites that charge a fee for their use.
Checkers