1. A tissue imaging system comprising: an imaging unit configured to create an object image with information of oxygen saturation of a blood vessel; an area determining unit configured to determine a lock area within said object image; a location updating unit configured to update a location of said lock area according to motion of said object at each time of creating a frame of said object image, said location updating unit executing: a landmark point extracting process to extract first landmark points from a first frame, and to extract second landmark points from a second frame created after creation of said first image, wherein said first and second landmark points are distinct from said lock area; a landmark point specifying process to specify part of said second landmark points whose feature value is equal to part of said first landmark points; a movement amount obtaining process to obtain a movement amount between said first and second landmark points whose feature value is equal; and a location changing process to change the location of said lock area according to said movement amount; a data acquisition unit configured to acquire said oxygen saturation in said lock area when said lock area is updated; a monitor image generating unit configured to generate a monitor image including acquired change information of said oxygen saturation; and a display unit configured to display said monitor image.