You are actually doing very well for not having a trainer :)
I like your position, really. It's not perfect, but it's definatly not dangerous, and not anything like I've seen in some self-taught jumpers. Here are just a few things I would address immediatly, if I were teaching someone with your position -
Your heels. They need to go way, way down. Yes, shortening your stirrups will help, but there is also the muscle aspect - sink those heels!! I would actually take your stirrups up 2 holes, not one. Then just picture putting all of your weight way way down into those heels. That will help a lot.
I would also reach your hands a little further up the neck. I can tell you are kind of relying on his neck, though, and that will hinder you from giving that really nice release that would make this picture even better. I would spend lots and lots of time in 2 point, with no hands! Make sure you are bending at the hip, just like you are in the pictures, with your heels way down, and don't come out of two point till you want to cry it hurts so bad. This is where it is really helpful to have a trainer - they will push you farther than you want to push yourself. But you need to do it - set goals for yourself! Make yourself do two point for an hour straight, no exeptions. It will dramatically improve your position in no time!!
After you have the good core that 2point will give you, really think about touching your pony's ears. It may be exagerated at first, but that's fine. I'd rather have an overexageration of a release than not enough, especially if you won't be competing. You can fix a 'too big' release later - but a 'too little' release and your pony won't jump for you. I don't think this is a problem at all here, especially since I can tell you value his mouth, but I'm just putting it out there :)
Overall you look wonderful!! I think after your shorten your stirrups 2 holes, a LOT of these problems will just fix themselves. Just practice practice practice, and you'll be great