Animal Ghost Pictures: Horse

Jason of the UK sent us this ghost picture. You will have to look close, but eventually a horse and rider can easily be seen:

"This was taken at my friend's horse training stables in Bury, UK in November '07. Apparently the horses go a bit wild sometimes and my friend decided to take some pictures. I highlighted what I see in Photoshop to make it easier. I see a male/soldier riding a horse carrying a shield."

The horse with rider are slightly darker and facing to the right. What looks like a shield to Jason appears to us as an arm. Perhaps the rider is wearing armor and helmet?

What do you see?