The old URLs fetched the image from plt-scheme.org. That website is no
longer up, and it's better to host all images locally anyway.
I was able to retrieve the right PLT Logo from web.archive.org via:
wayback_machine_downloader --all-timestamps plt-scheme.org/logo.gif
That command fetched three copies of logo.gif, all of which were
identical. The image is now committed to this repo as plt-logo.gif.
Please note that there's another, different plt-logo.gif in the misc
directory.
Lassi Kortela