— In this paper, the concept of ultrasound image-based force enhancement is introduced. It consists of a robotic comanipulation system that assists a surgeon performing an ultrasound exam through a minimally invasive access. The robot is programmed in such a way that the surgeon's feeling of the distal contact between the probe and the organ is enhanced, despite disturbances raising from interactions with the trocar or the natural orifice through which the probe is inserted. Contrarily to existing approaches for force enhancement, the proposed method does not require any distal, nor proximal force sensor. Rather, forces to be applied by the comanipulator are computed from the measurement of the organ deformations in the ultrasound image. In the paper, an example application to computer-assisted prostate biopsy procedures is given. A first implementation of the concept is then presented, involving an endorectal ultrasound probe and a one degree of freedom robot. In vitro experiments validate that the proposed mode of assistance significantly helps the detection of contacts between the probe and a balloon simulating a prostate despite large friction disturbances.