It is unlikely that a single photograph can be successfully cropped in different ways, so tell the photographer in advance how you intend to use the photographs. For instance, the example below is not ideal for use as a header: for this, the photographer needed to have taken the photograph from further away, so that the student in the background would fit better within the header frame.
If you are ordering header images for a responsive website, the main subject must never be at the right or left edge of the photograph. Make sure you clearly inform the photographer if photographs are to be used for header images. The photographer will then take wider shots, so that the correct ratio is displayed on all devices.