Thank you for your answer.
Maybe my question wasn't well formulated: We do not have many pictures, but only one single picture, plus exact camera position and many ground control points. We are not necessarily interested in a 3D reconstruction of the scene for now, but rather in retrieving the camera calibration.
As described, I have successfully imported the picture, set the ground control points. But "align photos" or "optimize cameras" is greyed out, i.e. cannot be run.
As I've said, for now we would like to retrieve camera calibration. I know this is probably not what most users want to achieve, but maybe someone has an idea or hint, how this could be achieved using metashape?
(A regular camera calibration cannot be performed, these are remote webcams and cannot be accessed or removed)