1. An image display device that displays acquired image frames, comprising: an image processing unit that detects a target in a first image frame among the image frames, generates, based on a result of the detection of the target in the first image frame and a result of a detection of the target in a fourth image frame that has been acquired before the detection of the target in the first image frame, a first prediction parameter containing a first predicted location of the target in a second image frame acquired at a first time when a predetermined number of frames or predetermined period of time has passed since the first image frame is acquired, detects the target in a third image frame acquired at a second time that is between the acquisition of the first image frame and the first time, and generates, based on a result of the detection of the target in the third image frame and a result of a detection of the target in a fifth image frame that has been acquired before the second time, a second prediction parameter containing a second predicted location of the target in the second image frame; a script processing unit that generates, based on the first prediction parameter, a first tracking image such that the first tracking image continuously moves over a plurality of frames between the first and second image frames, starting from a starting-point location of the target in the first image frame and heading toward the first predicted location in the second image frame and, when a difference between the second and first predicted locations exceeds a predetermined threshold value, stops generation of the first tracking image and generates a second tracking image such that the second tracking image continuously moves over a plurality of frames between the third and second image frames starting from the location of the target in the third image frame and heading toward the second predicted location in the second image frame; a synthesis unit that generates combined images where the first tracking image is put on the plurality of image frames between the first and second image frames and generates combined images where the second tracking image is put on the plurality of image frames between the third and second image frames; and a display unit that displays the combined images.