Hi Kirk,
That's pretty much what I thought.
And this is just me talking here. This may be a giant deal to some stakeholders. But as far as I'm concerned, given the issues that happen downstream when publishing CMSes get ahold of the picture and the strong/neigh on to absolute need to be explicit about the time element in the caption on historical photos, it's not urgent by any means. (I have just used January 1 in this case for decades.)
That said, when the time comes, I'd vote for some sort of tickbox to temporarily turn off date validation or another choice in the flyout for what type of date the user wants (Today, Date Created, Date Modified, etc) for "Year Only" or something similar.
Cheers.
-Carl