Shareability · 18 points
og:image
One check, stated three ways: what we measure, what would make it wrong, and how to confirm it yourself.
What this measures
Whether og:image is declared, resolvable, and — since v4 — whether the image actually answers. We send a HEAD request to the URL and read its status, content type and declared size, next to any declared og:image:width/height/type.
Where this check can be wrong
HEAD is optional in HTTP: a host that refuses it is recorded as unmeasurable, not as broken, and you keep the credit. We also cannot see how a platform crops your image, only that the file loads.
Verify it without taking our word for it
curl -I $(grep -o 'property="og:image" content="[^"]*"' <<< "$(curl -s https://your.site)" | sed 's/.*content="//;s/"//') — status first, then the platform preview tool.