Hehe, I sometimes forget this is Australian! 
Licenses are a vast field and it’s very complicated and very expensive
I think that even royalty free does not mean that you can use it in commercial projects. You need an explicit commercial license. And yes in most cases it is very expensive.
Your case is special, as a collage of many images will of course cost you a ton of money.
What most people here do is that they buy simple licenses and used images in their Previews. Then the downloadables only have image placeholders.
Personally I don’t like this, I prefer to be able to sell What I am showing in my preview. But I do understand that this is complicated, especially if images of people are involved.
That’s why, as I said above, I spend a lot of time chasing commercial use images.
I’m not sure if it’s acceptable to link to outside resources on this forum? Otherwise I’d leave a few tips here.
You can always mail me through my profile, I’m happy to share my resources with you. Beware though, no magic there, I’m always on the lookout and always chasing myself.
It’s not so difficult finding free commercial license imagery. It is however very difficult to find free commercial license imagery of outstanding quality.
And no, I don’t think cutting an image in half will give you any leeway under licence … On the contrary, many images have a licence which does not allow you to alter them in anyway.
Licenses and copyright law are an ocean!
Cheers
Chris