I usually take photos too, my work being too large for our scanner.
The rear hock is ok, it's the rear pastern/fetlock joint that isn't in line with the lower leg bone, as it should be. Look at the way you drew the front leg which is bent back. That is more correct and the rear leg will function the same way in the pastern joint.
Overall the porportions are good, the head a tiny bit small and the ears are bent in the wrong direction. Really look at a horse with his ears pricked forward and you will see that the bend in the ear is the opposite form what you have drawn.
If you have a chance , look at a horse skeleton diagram and it will help you see how to pub the "meat on the bones".
Very good start.