There is another great resource at:  http://www.shorpy.com/

The site includes thousands of mostly black and white photographs in high-resolution digital form.  They are arranged in galleries like:

Civil War
Dust Bowl
Japanese American Relocation
Kids (this includes child labor images)
World War I
World War 2
The Depression

You can scroll through all the galleries here:  http://www.shorpy.com/image

Here are a few examples of the images (click on the title to go to the image, then be sure to  click “View full size”):

The Unnamed Soldier:  1864
Auction & Negro Sales:  1864
Abraham Lincoln:  1865
Mold Boy:  1909
Back From the Front:  1918
Cimarron:  1936
Angel of History:  1942
Angel of History:  1943

What are some (from these lists and/or elsewhere on the site) that would be especially useful in your teaching?

Alythea