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Oof, tough problem. This may not work very well, but I have some options.

First, is it possible to shine a light through the back of the hole? That would make things very easy.

Second, the screw has the small white reflection in the bottom of the slot. This will only show up on some screws, so it's not reliable. But if you can cause it to be seen consistently, it's a good feature.

Third, the one with no screw has a yellowish tint to it. You could use that to classify. Take the average color and if it's on the yellow side, it's empty. This may need to change based on what's behind the screw.

You can also combine two and three.