The top of the photo is toward the withers, no? All in all, looks like even sweating is going on. The only thing I see, and not sure of this, it looks like the rear of the saddle may be swinging side to side some as the horse moves. The hair is moved back and forth.
I'm not super experienced, but it looks like their right side is their strong side. See how the left side (right side on the horse) is darker? I THINK that means there are more muscles, therefore the saddle fits tighter on that side, therefore their strong side is the right side.
My guess is this saddle is either placed too far forward or its slightly too narrow at the shoulders since it's sitting cantle low. The marks show much darker marks near the back of the saddle, so that's where most of the weight is when a rider is up there. When this saddle is on the horse, is the cantle higher than the pommel or even?