A robotic surgery system 10, comprising: a surgical tool (26, 146, 250) having a plurality of features defining a first marker (140, 150, 170, 190, 240, 260, 265), the plurality of features comprising an identification feature defining first information and redundant information, the first information identifying the first marker (140, 150, 170, 190, 240, 260, 265) and the redundant information also identifying the first marker (140, 150, 170, 190, 240, 260, 265); an imaging device (28, 86, 114) for capturing a first image of said tool (26, 146, 250) during use and for outputting first image data in response thereto; and a processor (58, 116) coupled with the imaging device (28, 86, 114), the processor (58, 116) adapted to process said captured first image data so as to: determine positional data for the first marker (140, 150, 170, 190, 240, 260, 265); determine an identification of the first marker (140, 150, 170, 190, 240, 260, 265) by using the first information of the identification feature; validate the identification of the first marker (140, 150, 170, 190, 240, 260, 265) by using the redundant information of the identification feature; and determine tool state data for the imaged tool (26, 146, 250) by using said first marker positional data and said validated identification of the first marker (140, 150, 170, 190, 240, 260, 265). a surgical tool (26, 146, 250) having a plurality of features defining a first marker (140, 150, 170, 190, 240, 260, 265), the plurality of features comprising an identification feature defining first information and redundant information, the first information identifying the first marker (140, 150, 170, 190, 240, 260, 265) and the redundant information also identifying the first marker (140, 150, 170, 190, 240, 260, 265); an imaging device (28, 86, 114) for capturing a first image of said tool (26, 146, 250) during use and for outputting first image data in response thereto; and a processor (58, 116) coupled with the imaging device (28, 86, 114), the processor (58, 116) adapted to process said captured first image data so as to: determine positional data for the first marker (140, 150, 170, 190, 240, 260, 265); determine an identification of the first marker (140, 150, 170, 190, 240, 260, 265) by using the first information of the identification feature; validate the identification of the first marker (140, 150, 170, 190, 240, 260, 265) by using the redundant information of the identification feature; and determine tool state data for the imaged tool (26, 146, 250) by using said first marker positional data and said validated identification of the first marker (140, 150, 170, 190, 240, 260, 265). determine positional data for the first marker (140, 150, 170, 190, 240, 260, 265); determine an identification of the first marker (140, 150, 170, 190, 240, 260, 265) by using the first information of the identification feature; validate the identification of the first marker (140, 150, 170, 190, 240, 260, 265) by using the redundant information of the identification feature; and determine tool state data for the imaged tool (26, 146, 250) by using said first marker positional data and said validated identification of the first marker (140, 150, 170, 190, 240, 260, 265).