I’ve actually worked with real-time image processing, so I can tell you right now that with multiple cameras you can easily get millimeter precision. My only doubt is picking the exact frame, like, right when the ball leaves the player’s foot on the pass. I haven't checked, but I heard they have pressure sensors inside the ball now to nail that exact moment. But honestly, even with all this tech, I agree there should be some margin for error. There's no way players can be sure if they're offside or not.