These approximately 3-1/2" x 5-1/2" cards take their name from the fact that they are printed versions of some of the photographs that appear as the central portions of the 1911 T5 Pinkerton cabinets. It's unknown whether these latter-day cardboard versions have any connection to the "real" Pinkertons, and the checklist for this type is considerably shorter, with fewer than two dozen known players, compared to more than 300 known T5 cabinets.
These cards can be found with score cards printed on back, with postcard backs, or with blank backs. The score card versions are considerably scarcer than the others, and valued at about 2X.
The 2010 Standard Catalog of Baseball Cards lists blank/postcard backs at $150 in NM, $75 in EX and $45 in VG, with typical Hall of Famers at $250, $125 and $75. Superstars like Matty, Wagner and Cobb currently carry values of $350-1,500.