OK, so the problem is PNG files. Sort of.
A couple of weeks ago I lowered the overall image size parameters to try and prevent the picture uploads from consuming all the disk space on my server. One of the things I changed was the max image size which I changed from 2 MB to 1.5 MB.
Now, some quirkiness about the system needs to be explained because it's, well... quirky.
That 1.5 MB file size is not the size of the file you can put on the system, but rather the size of the file *after* the system converts it for local storage. All images are compressed when they're put on the system and the file size after the system compresses needs to be under 1.5 MB or it will be rejected. That's what's happening here.
Those two pics of Nixie tubes look the same, but one was a 10 MB jpg and the other was a 2 MB PNG. The 10 MB JPG file uploaded fine but the smaller PNG file failed. Why? Because PNGs don't compress as well as jpgs. Here's how the system compressed those files:
10 MB JPG -> 172 KB
2 MB PNG -> 1.6 MB
Since I had set the limit at 1.5 MB, the PNG failed while the seemingly much larger JPG worked.
As for PDFs, the system doesn't compress them because they're not images (settle down, Ralf
) so when the PDFs in question were moved to the system they were rejected because they are 2.3 MB which is over the limit. It's not a good idea to use PDFs for images because any compression of the image was done while making it a PDF and the system can't deal with that.
The PNG thing is kind of a bummer because Mac screenshots are PNGs, but at the rate we all collectively upload images changing that limit from 1.5 MB to 2 MB has a pretty serious impact.
