A method and apparatus is provided for auditing cartridges and empty cells in a storage library system including a plurality of cells for storing cartridges and further including a robotically actuated hand assembly. A line-scan camera is secured to the hand assembly, and a visible pattern is positioned within each cell such that the visible pattern is readable by the line-scan camera when the line-scan camera is moved to a position adjacent the particular cell if the cell is empty. The visible pattern is positioned such that the presence of a cartridge within the particular cell would prevent viewing of the visible pattern within the cell by the line-scan camera. The line-scan camera is operated in a manner to search for the visible pattern within each cell for auditing numbers of cartridges and empty cells in the storage library system.