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Detect presence/absence of a screw - Image comparison

Hello community,

since several weeks I'm sitting on a problem of object verifications and cannot get sufficiently good results. The task is to check whether a screw is in a hole like seen here:

Image with screw

Or not:

image description

I'm using OpenCV 3.0 through Java and the method I have tried a lot is Feature-Matching through an ORB detector and comparing the number of successful matches in the area where a screw is supposed to be. However, the result is overall fairly unreliable and fluctuates a lot from an image to another (taken live with a camera) even if there are just seconds between the shots and the image is blurred slightly against the noise.

Additionally, the system doesn't seem to get any grip of the actual shape of screw. The features are too small...

Does someone have an idea what other method I could use?

Huge thanks in advance :)