The Horse   

Here's Muybridge's horse as a "GIF89a" simple animation

The major subtlety in stitching the original picture together on a modern computer is the question of reference point. The arrangement Muybridge used although effective and well thought out, was scarcely up to today's common photographic standards. To translate "individual frames" from separate cameras each adjusted slightly differently, is not easy.
Which part of the scene is the "centre"?
The horse moves and flexes and the rider moves arms, shoulders and legs in balance.
In this case some applied horsemanship comes in useful, and using the centre of gravity of the rider (which moves vertically mostly) as a reference point seems to give acceptable results which are not otherwise achieved.

For more on horse movement, see "The Nature of Horses" by Stephen Budiansky (Weidenfeld & Nicholson, London, 1997): ISBN 0 297 81779 5

This is, of course, an Acolyte site design