I did some small internal changes, normally not visible, to handle vehicle numbers above 999999, as we'll soon reach that.
The site was not originally intended to list so many background vehicles, so there was no reason to reach the million of entries some day (there is far from a million of vehicles listed, of course, but the deleted vehicle entries numbers are not re-used).

If you notice any error on the site, please report them, as there may still be some that I missed.

I've added several images successfully tonight, but am all of a sudden getting error messages that the image I'm trying to add is too large. It's happening on every image; they're the same size as every other one I've added.

Related?

Normally no, but maybe you added one while I modified that page and the option "automatic resize/recompress" was unchecked after that?

Ah - yes, that was it!!