A probe for measuring features in inaccessible locations comprising an elongate body adapted to be inserted into said inaccessible location, a probe tip being defined at a distal end thereof, a light source for transmitting light from said probe tip to illuminate a surface adjacent the probe tip, an image sensor for generating an image of the surface adjacent the probe tip and image processing means programmed to carry out digital imaging correlation upon subsequent images generated by said optical sensor to determine the motion of the probe tip.
