Possible ways to determine the direction of moving object?
If your images are as clear (I specify clarity here because it is easy to threshold in this case) as your examples here, one easy way of computing the direction vector of a moving object would be to calculate its center of mass across frames. 

For this it's as simple as thresholding first (pixels which are part of the object are equal to 1, all other pixels in the background are 0), then taking the average x-coordinate of these set pixels. Find this average x-value for all your frames, and just take the difference between consecutive frames. You determine whether a positive difference corresponds to movement in the left or right direction.