Below are specialized collections focusing on U.S. or Western U.S. contents, but there are many other digital collections of images from libraries and museums worldwide. You can often find these digital collections by searching online.
Buffalo Bill's Wild West Show and Congress of Rough Riders of the World - Circus poster showing cowboys rounding up cattle and portrait of Col. W.F. Cody on horseback. 1899.
Copyright 1899, Courier Litho. Co., Buffalo, N.Y. ; copyright expired.