I have been using a canon pixma MP560 ink jet to print my decals.
I use decal paper designed for the ink-jet printer. After allowing the ink to dry you clear coat it a few times to protect the ink.
I set the printer settings to photo, glossy paper, and vivid photo in the different set up screens.
The results have been mixed but over all I am happy.
You have to use white backed paper to get any type of color coverage on dark cars. Just change the background color to match the car color.
I still have tons to learn as I am just getting started.