Well there are a few things I see here but they are ALL easily corrected with time in the saddle. First thing I noticed (which is already stated above) is that your stirrups could be shortened a hole or two. They look good in the 3rd photo! But the others they look too long. When you stirrups are too long it makes it harder for you to keep you legs anchored and under you. That may be why you legs have slipped back in some of the photo's. The only other thing I see is that in some pics you haven't released your horses mouth enough. The 3rd and last photo are the worst ones. Just remember to soften you hands a little as you jump and give your horse more a a release.
O and a tip! I used to have the "chicken elbows" too when I started riding! Lol (In your pics it looks like your squeezing you hands together, almost palm to palm especially in the 2nd pic) A good way to remember to keep you elbow's in is when approaching each jump, is to tell yourself to reach up in a forward motion like you going to give his mane and neck a good scratch! Or visualize yourself pushing something away from you. It will help keep your elbows in towards your sides a little better and allow you forearm to reach up a little more, also helping with a good release on his mouth. Hope I've helped!
I love this picture - Love how your arms are out - makes me think of the Titanic. Love the pink as well :) :)
The biggest issue I see here right now - is way to over active of an upper body.
You are really collapsing your upper body, and there is absolutely no reason to do this. I can see if your horse has a huge scopey jump, and you are doing 5'0" fences - but aside from that, you must always allow your horse to do his job - not the other way around.
We must learn to ride our horse, not the fence. Anticipation of the fence is a big error riders make - they focus on it, they race to it - and they quickly forget the most important factor ..... our horses.
What you are doing, is really focusing on the fence infront of you - instead of your horse. Learn to ride your horses rhtym - what I highly recommend is doing Lunge Line Work, with no reins.
Really work on where your leg is, your seat is, your upper body is. Really work on controlling your horses rhythm through your seat and legs. Then, as you are doing in the picture I like - work on riding your horses rhythm and waiting for his motion to lift you out of your tack, while going over trot poles and cavaletti's.
I do this, this is a great exercise - so that you can really focus on rhythm and where your body is at all times.
Sit, sit, sit, sit - wait for your horse to lift you - remain with your horses motion and center of gravity instead of lurching yourself forward.
When you lurch yourself forward, and collaspe your upper body like that - you are throwing all your bodies weight onto your horses forehand, making his job that much harder.
When you are going over these small fences, really work on sitting and waiting for your horse. Allow your horse to do his job. Remember, ride your horse, not the fence.
Our job, is to ride our horses to the base of the fence in a rhytmical, steady, strait tempo. Our horses job, is the rest.
Now the other thing to work on - is really opening up your legs and allowing your bodies weight to flow down into your heels. Your leg is good, but it could be better.
We want to remember that we are not ontop of our horses, but wrapped around them. Re-estabslish your leg by using your inner calf at the girth, your heels are good right now, in the last 2 pictures - but work on getting yourself around your horse.