Attaching wooden pictures

I have some wood framed posters and I need to attach them all to a larger piece of wood to hang on a wall. Im not sure what the best way to attach them would be. I can't nail them because you would see the nails. Is there a very strong glue that would permanently hold up to 3 kilos? Also what sort of wood do you think would be best for the backing board that I attach them too? Thanks