imagesbw = Binarize[MedianFilter[Image[ImageData[#][[All,All,1]]],4]]&/@images;

movement = ComponentMeasurements[#, "BoundingDiskCenter"] & /@ imagesbw;
tracking =
 Graphics@Riffle[{Red, Orange, Blue, Red},
   Point[Cases[# /. movement, x_ /; Dimensions[x] == {2}]] & /@
    Range[4]]