I worry to see your horse tied to a barbwire fence by the reins, with a curb bit. A lot of danger there.
The saddle looks like it is too narrow in front, thus it slide back. It's hard to say because the white horse kind of disappears into the back ground.
IF you really want accurate opinions, take him to level ground, in good lighting and get someone to help you. PHoto him with NO pad on and from various angles.