So what is the difference between a Ground Control Points (GCP's) and Check points (CP's).
Simply put GCP's are used to georeference and align the photogrammetric data during processing to ensure the accuracy of the output. CPs are used after processing to verify the accuracy of the final results.
Changing some of your GCP's to CP's give your client faith in your results.

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GCPs should always be:

1.            Large enough to be seem in a drone image.

2.            Easily identifiable from any orientation.

3.            Have a colour contrast the stands out on the image.

4.            Must have a clear, unambiguous centre point.