I think the photo of him sitting in the shower was taken right after she began to threaten him with the weapon, holding whichever weapon in one hand, and the camera in the other. She forced him to sit in the shower at gun-or-knife point, knowing that he couldn't put up much of a fight while sitting. She fumbled the camera because it was being held in one hand (I have a Canon that is very similar to the camera Travis owned, and it's possible to hold it in one hand and make photos, but it's awkward.) She was left handed, so she would have held the weapon in the left hand, and the camera in the right.
The one thing that perplexes me about the photo of Travis sitting in the shower is why it's only of his body and does not include his face. I think this is because Jodi was shooting the photo with only the right hand, while she was threatening him with the weapon in the right. I wish it would have included his head, because I am sure he was in utter terror by that point in the "photoshoot."
I think he was aware that Jodi was taking photos of him in the shower, because the flash is on in several of them... you can see the shadow cast by the shower-water droplets.