1. An analysis method for a surgical operation via endoscopy at an operative site in a volume located inside a body, the method comprising: a) selecting the surgical operation to be performed; b) detecting from an image of the operative site at least one instrument present therein, c) detecting from the image of the operative site at least one portion of an organ in the vicinity of the detected instrument, d) determining the positioning of the detected instrument relative to the detected organ, so that the detected instrument, the detected portion of organ, and their relative positioning form parameters defining a detected surgical step, e) selecting in a database a conceptual surgical step corresponding to the detected surgical step of the selected surgical operation from the detected instrument, the detected portion of organ, and their relative positioning, f) comparing the parameters of the detected surgical step with the parameters defining the selected conceptual surgical step to determine the differences between these parameters, g) (i) comparing the parameters of the detected surgical step with the parameters of a step consisting of at least one past performed surgical step derived from at least one same surgical operation as the selected surgical operation performed previously from a different patient, (ii) wherein said at least one past performed surgical step derived from at least one same previous surgical operation from a different patient is stored in a database with the conceptual surgical steps to make a comparison, h) displaying an overlay image on the detected image from an endoscope showing a current position of the detected instrument and the detected organ, to indicate an optimal position of the instrument, i) automatically varying in real time the overlay image based at least on step (g); and j) providing information on the quality of the detected surgical step on the basis of determined differences.