Soldier flag - making waves

The current design for the flag with soldiers and poppies on it is static and not very interesting because the flag is flat ad doesn't have any ripples in it. I've been wondering for the last few days as to how I could do this, because I don't know any fancy Photoshop techniques that can put this kind of effect on the flag design.

I searched up tutorials online, and followed on to wrap an image around another existing image (called mapping, in which I used an image of a plain white flag with ripples in it off the internet to be the base image to wrap my image of soldiers-poppies/NZ flag onto). This didn't really work at all. Here is my failed attempt.

How do people make a simple ripple appear through their image? I'll have to keep looking.