An interesting thing I’ve figured out while playing with these animated gifs is the importance of picture alignment. If the pictures are simply swapped, it sometimes only adds movement. In this example I aligned the picture frame in the top left portion of the picture. you can see how much difference in overlap the photos have by the edge of either picture.
To achieve reasonable alignment, I changed the opacity of the layer to 50% while I was positioning it, then after I had positioned it changed it back to 100%.