You cannot claim copyright on an image you merely own. The copyright owner is the only the creator, or perhaps another in a work for hire case. Simply because you own something that no one can legally claim copyright in doesn't give you the right to claim it. You have to be the creator of the work, this is the authorship requirement.
Doing "plenty of things that contributed to the end image" isn't the law, nor should it be, for establishing copyright. Should every photographer's assistant hold copyright for images the photographer took simply because he set up the camera for her? Should a production assistant hold the right for a film because he did some work to make sure things went well on set?
The arguments do make the use of the image more correct if it is established that the image is in the public domain.