Artificial tactile sensing is still underdeveloped, especially in sensing shear load, incipient slip, and total slip on a contact surface. These are very important for a robot hand to manually explore the environment or perform a manipulation task such as grasping. In this paper, we introduce a new method of detecting the normal, shear and torsional load on the contact surface with a GelSight tactile sensor . In addition, we demonstrate the detection of incipient, partial and total slip. The method consists of inferring the state of the contact interface based on analysis of the sequence of images of GelSights elastomer medium, whose deformation under the external load indicates the conditions of contact. Results with a robot gripper like experimental set up show that the method is effective in detecting interactions with an object during stable grasp as well as at incipient slip. The method is also applicable to other optical based tactile sensors.