As far as id guess... the artwork is 3d... so it would have needed to be photographed... rather than scanned. Depending on the photographer, camera, and lens... you probably will always get perspective distortions.
Even if it was spot on..its still only 2d... and does not accurately portray the arcade machine. Stereo 3d artwork should exist.
It can be as simple as taking two photos... and having a 3d display option set. Afaik... there is no stereo 3d output in mame...nor even the most basic multichannel sound output options yet.