The images are taken from a site that is dedicated to presenting and and preserving Plains art, drawings on paper, from the late 19th century for research and enjoyment.
One of the most beautiful albums:
Plains Indian Ledger Art.Native American art in ... accounting ledgers.'Beginning in the early 1860s, Plains Indian men adapted their representational style of painting to paper in the form of accountants ledger books. Traditional paints and bone and stick brushes used to paint on hide gave way to new implements such as colored pencils, crayon, and occasionally water color paints. Plains artists acquired paper and new drawing materials in trade, or as booty after a military engagement, or from a raid...' via plep