So in case you have images up for licensing or have something super popular, you have a serious leg to stand on if things get fucky with someone stealing the image.

https://eco.copyright.gov/eService_enu/start.swe?SWECmd=Start&SWEHo=eco.copyright.gov

cool, thanks OP

Do you have a link to the documentation on how this works? I stopped registering photos a few years back, specifically after they changed the rules and stopped allowing mass photo registrations.

I would like to back register my published photos for the past several years, and would be willing to pay $55 x each of the previous years.

Older article but Petapixel goes through the process 

Yeah, I know how to submit photos, and it is actually the same process since I last registered.

But a few years back they increased the price and changed limits for unpublished photos, specifically the whole concept of a 'collection'.

Anyway, I'm trying to get an understanding of how they're treating that published photos and 750 limit. They're not very clear on this. I may just zip up the 600 pixel wide photos that I published last year and see if they accept it.

Oooooh okay.  Unfortunately, I haven't gone through the process yet myself, so I'm not entirely sure.  I knew about it, but just looked it up the other day for the first time.