A great many donations of photographs and slides were made to groups like Marine Society and World Ship Society long before the dawn of the internet and website's like this. At that time it was seen as the best way to enable others to enjoy the collection. It is a shame that now there are so many ways to share these collections, the custodians feel constrained by worries about copyright, ownership etc., which results in the collections not being shared, which is probably the opposite of what the donor originally wanted.
I have scanned all my slides and photographs, and donated the originals to the WSS, while retaining the scans. However I've told WSS I'm quite happy for them to use any material as they see fit, with suitable acknowledgement, while I retain the use of the scans, including posting on here. Because I've taken them myself I see no problem.
However the current debate is if this particular site is an appropriate site for archive material not personally photographed by the poster. I think it is, subject to the copyright proviso, but it is obvious that others have different views.