There are other threads here about this, but you pretty much have to hack the infotainment system to change picture, but with the hack you can do all kinds of other cool stuff:
http://www.lukasz-skalski.com/portfolio/mazda-media-player/
Scroll down to see all the changes you can make, or not make if you choose, like getting rid of the warning screen at startup.
It is also completely reversible if you don't like it.