1. A device for detecting a surgical tool in an image, said surgical tool going through an incision made in a patient's skin or one of patient's organs, the device comprising: means for storing shape parameters of the surgical tool; means for determining a position of a projection of the incision in an image plane; and means for analyzing the image and detecting, taking into account the shape parameters and the position of the projection of the incision, points and/or straight lines characteristic of the projection of the surgical tool in the image.