Thanks to you for your suggestion, Evgeniy, and to those who have commented.
Kyle and Pieter have neatly summarised the normal policy. For normal ship categories where the images do not meet the genreral site standards (eg do not include the whole ship, there is an obstruction or it is not sufficiently sharp), ships which would otherwise be unrepresented on the site may be added, on the understanding that such photos are liable to be deleted if fully-acceptable images are subsequently added. They should be endorsed "only one on site" in the Photo Description box.
For newbuildings, ships still uncompleted are expected to be added and obstructions are permitted provided they they are part of the shipyard operation and are not excessive. There is no need for such images to be placed elsewhere, and they can already be retained indefinitely.
I do not think that there is a particular issue with IMO numbers. All members are expected to research the correct number before uploading their photos (noting that many vessels do not have one anyway), and the knowledge and interest of members, especially Corrections colleagues, usually resolves issues over confirming the correct number where there are errors of information was not found.
So I am not really sure what kind of photos you think would go into any separate category. Personally, I do not think that we should be extending our scope to add very poor photos, just because some vessels are not already represented.
Perhaps there is an important point that I have missed - please let me know if I have!
best wishes
David