I agree, but it's the same with your photos, my photos and anyone else's photos - they are the property of the individual concerned, and any photo posted on a web site without prior permission of the 'owner' is potentially infringing copyright laws, even if a copyright watermark is shown, or a credit given.
Many 'owners' won't mind if a credit is posted also, but there are, for example, avaition magazines who are fed up with the unauthorised use of their material, and are pursuing the infringements.