I wasn't going to post this but figured I'd get some thoughts anyway. No postwork as I'm going to rework the render. I added some Instant Iray Zombies to this not realizing that they wouldn't cast any shadows at all, along with the fact they look very flat which totally ruins the image I think.
I don't have that set, but I do have insta-billboards. I tested it and they did cast shadows using IBL lighting. A distant light created some weird effects, such as shadows cast into the space behind the billboard. I didn't try a mesh light.
Thanks for posting, though. It's a very cool render!
yah, maybe blur them a bit, some depth of field. I would try and take the shine of the clothing. Background is really busy, but it's zombies, they don't hold still on command lol, I but maybe a little in camera depth of field setting, some more diffuse lighting. Just what I might do, that's all, not a professional