I think you're off to the right start regarding your lower body. Your leg is in a good position at the girth and not sliding back (mine do...really bad habit that needs fixing! Haha) and I like your elbows a lot. You really don't need much release at all at a cross rail, so I don't think "sliding your hands up more," aka, a bigger release, is necessary at this time.
When you up your height past cross rails and 2', start thinking about how it would feel if you were the horse being asked to jump and lengthen your head and neck on such a tight rein. You want to give a generous enough release in that case so that your horse can have his head over that higher jump, and so you won't bump him in the mouth during or after.
The only thing I really see that needs changing at your level is your round back and shoulders. There's a lot to think about while jumping - strides, distance, rhythm and for you...equitation. Proper equitation means correct riding and happy horse. Fixing something equitation wise means consciously thinking about it when you need to do it. Take flat work for example...you notice your elbows getting straight. You think to yourself, "bend your elbows." You have to direct yourself to do so. Same thing with flattening your back. Really attempt over those jumps to bring your shoulders back and close your shoulder blades.
I agree with the above poster about your confidence level being related to height. I think your back and shoulders look great over the cross rail! You start to hollow once you get to the verticals, which says to me "confidence issues," as well.
Like I said, I'll reiterate that I think for just starting, you're off to a great start. Most things will come to you after lots and lots of practice and repetition. It won't happen over night, or in a week...it may even take months to get where you want to be. But go at your own pace and get confident enough to jump those verticals. Be patient with yourself! You are learning and it's quite the process. Remember, everyone rides a little differently and everyone learns a little differently.