1. A method for detecting an object, and determining a a mark count of the object, comprising: using a conveyor having motion relative to a two-dimensional field of view to transport the object; inputting an encoding signal responsive to the motion of the conveyor, from which can be obtained at desired times a corresponding encoder count indicating a relative location of the conveyor; capturing a plurality of frames, each frame of the plurality of frames comprising an image of the two-dimensional field of view; choosing, responsive to a first analysis of the plurality of frames, a plurality of active frames from the plurality of frames, such that the first analysis indicates sufficient evidence that the object is located in the field of view for each frame of the plurality of active frames; obtaining a plurality of capture counts corresponding to the plurality of active frames, each capture count of the plurality of capture counts being responsive to the encoder count corresponding to a time at which the corresponding active frame was captured; computing, responsive to a second analysis of the plurality of active frames, a plurality of location values, each location value of the plurality of location values responsive to a position of the object in the field of view in an associated active frame as computed by the second analysis; determining the mark count of the object using the plurality of location values and the plurality of capture counts, the mark count indicates the encoder count corresponding to a time when the object was located at a fixed mark point; and indicating a location of the object by producing a signal at a report time that occurs when the corresponding encoder count differs from the mark count by a delay count.