1. A method for depicting a tool or implant with respect to an image for surgical guidance, the method comprising: establishing a surface boundary for a region of interest depicted in the image; determining a position of the tool or implant with respect to the surface boundary; and displaying a representation of the tool or implant on the image, wherein a first portion of the tool or implant inside the surface boundary is depicted in the representation with a first degree of transparency that is different than a second degree of transparency or opacity of a second portion of the tool or implant outside the surface boundary, and wherein the first portion of the tool or implant is depicted in the representation with a plurality of degrees of transparency based on a distance inside the surface boundary such that the degrees of transparency increase to become more transparent as the distance inside the surface boundary increases.