Two features on frames Z324 and Z325 show blurs. They are the partition between operator and passenger compartments and the small white object immediately above the head of President Kennedy. Viewing following frames reveals that white object as the tip of the gloved hand of Mrs. Kennedy.

Stepping from frame Z324 to Z325 shows two changes. The partition becomes clearer and the hand becomes blurrier. A closer examination shows most images on frame Z324 are blurrier than on frame Z325. Further the blurrier images show lateral streaking. These characteristics indicate movement of the film with respect to the incoming light during exposure caused the blurring. By contrast, the movement of Mrs. Kennedy's hand by a few inches between frames Z324 and Z325 shows intrinsic motion as the cause of its increased blurriness.

Frames Z325 and Z326 show Mrs. Kennedy is swiping her hand from the left side to the rear of the President's head. As she swings her hand, its direction of motion moves away from the plane of view and toward the line of sight. By frame Z326, Mrs. Kennedy's hand is speeding toward the camera and its motion causes less blurring. This observation illustrates another characteristic of blurs caused by moving objects. Namely the components of their velocity lying in the plane of view cause blurring.

A lesser movement of the film during exposure accounts for most objects becoming clearer on frame Z326.

Having completed the left to rear movement, Mrs. Kennedy starts lowering her hand. This change in direction of her hand increases the downward component of its velocity. Not surprisingly more blurring accompanies the considerable downward speed of Mrs. Kennedy's hand as shown by frame Z327.

A blur caused by a rapidly moving object enables calculation of two components of its velocity. In general the uncertainty in position due to blurring places an upper bound on the plane of view distance moved by an object during exposure. Knowing the exposure time permits calculation of the upper limit of two components of the object's velocity. This technique is especially valuable in evaluating brief motions such as Kennedy's forward and backward head snaps.