When we take a photo of a person we must, in theory, get that person's permission prior to taking the photo. We can then copyright the photo. When we take a photo of a landscape, do we have to get the permission of the landowner? Really what we are copyrighting is the artistic effect that we have captured in the photo. Copyright law is so confusing that I would say that your son, if he thinks it is important enough, should consult a Lawyer. In this case I would probably not copyright his museum photos as the artistic effect is the property of the museum. I am probably totally wrong and I really think you should consult a lawyer.
Note that the law varies from country to country around the world.
In the UK, for example, there is NO requirement to get someone's permission to take a photograph of them (though it may well be bad manners not to ask). Copyright is also automatic - it is not something you have to 'do' - if you press the shutter then the copyright is yours (if you are doing so as part of contracted work, the copyright may then automatically be transferred to your employer, but that's a matter for the contract).
With respect to landscapes, again no permission required - BUT where you stand to take the image matters! Any non-public space (and this does include things like shopping centres / malls, which are privately owned but with common public access) can have conditions of entry - and these can place restrictions on photography. The National Trust, for example, which owns / manages huge areas of UK land, has as a condition of entry to any of its land / properties that commercial photography requires a purchased permit.
Other countries will have different rules - so if on holiday, it's worth checking if anything will affect you.