Stating the blazingly obvious especially where it applies to archive photos/footage etc, sometimes that information is simply not available anymore.
I have posted photos in the last couple of days the origins of which I have no clue. I don't know who took them, when, where or for what purpose. Similarly it has just taken me three days to identify a particular shot as being Alyssa Miller by Ellen von Unwerth because it has become almost anonymous on the web, and the few instances of it I found had it unidentified and lumped in with a bunch of other material. A set of Scarlett Johansson pictures has all but vanished from the forum and the original poster does not have the full set anymore and has no information on them. There is no information attached to any identical instances of those images left on the web that I could find. So almost an entire set is gone outside better versions of the two that were left alongside the one addition I found.
Will you therefore remove all material that does not have this information attached? Penalise or ban members for not knowing? As propositions go that's pretty preposterous and will do nothing but serve to alienate contributors beyond regurgitating what they take from publicity and social media sites.
In short, while this idea might be thunderously convenient for you to check you aren't posting duplicates (because heaven forbid you should bother to scroll back a few posts to actually look for yourself), the only people it will really benefit are the cash whores posting for profit. Most of those classics shots and old scans will vanish.
There is a big difference between leading by example and hoping others adopt practices as a matter of course and courtesy and imposing a rule which must absolutely be followed. By applying and enforcing a rule which cannot necessarily be followed we will either limit the scope of what can be posted or will decimate the membership who cannot hope to live up to the new rules being enforced.
This is a community forum, not Getty. If you want information included I suggest you lead by example as I do, posting pictures and collections with date, publication, photographer and campaign WHERE I HAVE THAT INFORMATION, and see others pick up the habit [as indeed they are doing]. If you want information on picture or shoot then ask the poster. I they don't have the information, do a little research.
Trying to turn this into an enforcable rule is draconian, unsociable and downight unenforceable. It will kill the forum stone dead for all but a few people.
In my opinion.
BOC