I also noticed that some sites like this example https://cromwell-intl.com/travel/japan/wwii-cryptanalysis/?s=mb are quite picky about linking to their opengraph images.... .
Cryptanalysis and the Nuclear Bombs

The nuclear bombing of Hiroshima and Nagasaki makes more sense once Japan's internal communications were revealed after 50 years of official Allied secrecy.

Bob's Pages of Travel, Linux, Cybersecurity, and More

This is how it is rendered on fedistats 😅

I guess the reason is that I'm not actually saving all those pictures but linking from my page, and I guess external links aren't liked well... .

Although for me this is still better than keeping a copy of those pictures. Not sure anymore, though...