Most common aspect ratio?

Both/neither!

My work uses cameras for documenting tiny details on cars (cannot give more details), and uploads them to an internal system.  We're trying to update the system to not have black bars on photos (wasted space) as they're viewed on tiny screens.  But we buy cameras as and when needed, so we don't know what aspect ratio they'll have.  Does that make sense?

Thanks!

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Lost in the void between the concept and the execution.