There's a side note that could be added. I just tried to launch the script as a new user (not the usual pi user), and failed miserably. After some digging, I found that the user launching the script must be a member of at least the gpio, spi and video groups. When the user is part of these groups, the script can be launched, but it's still asking me for my sudo password (even if the script is launched without sudo), so I may be missing something.

@thomasdom It may be useful to add that the file omv-epd must be executable (chmod +x).