So what is the difference between a GCP's and CP's?
Simply put GCP's are used to geo-reference 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.
GCP's and CP's look the same on the ground and can be recorded in the same CSV file. Changing some of your GCP's to CP's give your client faith in your results.

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GCPs/ CP's 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.