It is possible to recover deleted stuff by hooking up his phone to a computer, but it takes a lot of programming and computer science knowledge that I unfortunately do not have. Plus it requires certain software that I, once again, do not know how to use. So since you don't really have a way of knowing how to recover these photos, then that kinda isn't an option.
If you want to find out who he is texting, you can always do the classic "look at his phone when he's not around" or something of that sort. There are once again software and programs you can use when you hook his phone up to a computer to track down all his text messages but I don't think that part is an option either.
So what should you do? Well if you are in a relationship where you feel like the other person isn't being completely honest to the point where you feel overly jealous and suspicious like this, then that should already be a hint to you that there is something wrong and you need to end it. If your relationship was healthy, you would trust your partner and he wouldn't continually do anything to raise your suspicion either (several times is okay since we're human, so the key word is continually). Therefore if I were you, I'd stop going through all that trouble of trying to find out who he's texting and the pictures he deleted on his phone and just get to the bottom of how you're feeling and why. Then take action from there. Most likely, it's best to just end things with him from here because it doesn't look like you're going to get anywhere far with an unhealthy relationship like this.
I know that it's easier said than done, but it's for the best. You deserve to have a more secure relationship where you can feel comfortable and trust your boyfriend. You said it yourself, you don't want to be dating someone who isn't honest. If your gut is telling you that he isn't being honest, then that means that something is up and it's most likely because your gut is right. I know that you're trying to find proof in your boyfriend's cell phone history order to justify your own feelings. Why do you need to justify your own feelings if it's making you feel uncomfortable? You don't have to be 100% right about this suspicion, but the fact that you are not feeling okay with this is already a good enough reason to break it off. You should never have to justify why you are feeling a certain way if it's bothering you!