You might want to check the maintenance manual for the specs, but sometimes you can tell by the amount of the manufacturers groove that is left on the pads (just above the end of the last 'W' on the photo). It's fairly typical for brakepads on any vehicle. Some will have a 'wear line' printed on the edge, and some will even change to a compound that begins to screech under braking. It appears that there is plenty of 'groove' left in the photo.
But once again, it's best to check the maintenance manual...