Ok, first off you are good. and i love my pic. you have a good eye for bacrounds, but it seems to me you are trying to make it look like the horse like it's 'in' the picture, But the way you are placing in it, it looks sloppy (please don't take offence) if you are trying to make it look like they are in the pic, you need to look at the animal's body language.
Now, if you trying to make the animal stand out more then the back pic, you should make the picture of tha animal take up more of the screen. But you do have a good nack for cuting them out, i hate cuting
It will take a while, but you will develop an "eye" just keep practicing!