An ink tank security system on a printer includes an ink tank connection station having a cavity with a passage for insertion of at least one ink tank through the passage into the cavity to supply ink for printing operations by the printer and for removal of the ink tank through the passage from the cavity for replenishing with ink. A door is mounted adjacent to the passage for undergoing movement between displaced positions enabling or blocking movement of the ink tank through the passage to or from the cavity. A sensor adjacent to the door is adapted to sense movement of the door between the displaced positions. A security device separate from the ink tank is insertable into and removable from a control slot on the printer under the door to control re-use of the ink tank for replenishing the supply of ink.