I have recently found twelve 4"x2-1/2" carte de visite in some postcards that I inherited from my grandmother. Upon researching them, because they had 2- and 3-cent US Internal Revenue stamps on the reverse, i found that they were made during the period of our Civil War.
The link above will bring you to some webpages displaying the front and reverse of them, and there will also be links where you can purchase a reproduction color print them, as they are way beyond copyright protection.
The photography studios represented by this small collection include: Bryant (Charlestown, MA), Joseph W. Warren (Fall River, MA), T.R. Burnham (Boston, MA), Knowles & Hillman (New Bedford, MA), H.F. Norton & Bro. (Fall River, MA), G.W. Venner (Charlestown, MA), Walker at Adam's Gallery (Worcester, MA) and S & S. Brown (Providence, RI)