I notice a series lines never seen before on my server access log that runs like this consecutively within the same one second:
PROPFIND /images/flag.jpg HTTP/1.1 405 493 265 511 - LibreOffice
HEAD /images/flag.jpg HTTP/1.1 200 164 - 229 - LibreOffice
GET /images/flag.jpg HTTP/1.1 200 186 338166 338395 - LibreOffice
It appears that copying images from the website to a LibreOffice document will cause these queries to be triggered. I found PROPFIND being mentioned on a Microsoft website, but still do not understand its usage and why not just use a single GET instead?