With a 24h watch, you line up the hour hand with the sun. Because the sun does a full circle in 24h and the hour hand does the same, lining them up will always make 24 point north (on the northern hemisphere).
A compass is still the better option, because the magnetic field also points north in the southern hemisphere and doesn’t have to be recalibrated when you move too far east or west.
Does that actually change the file, or will it still break when your software can’t handle webp? Because I did that to a webp, but Firefox still shows it’s a webp (in the tab name), probably based on magic byte. I don’t have any viewers that can’t display webp though, and I think they’re all smart enough to go by magic byte.