Hey robert,
Many Thanks for your quick reply.
Yes that is good, images must be still detected by discourse core like your plugin does even if they are hosted on external public sites. This is exactly what i want discourse core to support, where can i request this feature?
Basically all my topic images are loaded from other external public sites like imgur, https://pixabay.com/ and other free sites which allow us to use images for free. Im not using any object storage,
So i never upload the images on my own discourse server, to save my storage costs.
I use 3rd party free image hosting sites to show my images, let me explain you.
You can see e.g on my this topic https://howtodiscuss.com/t/how-many-carbs-on-keto/28069
e.g
that first image is actually loaded from imgur. You can see its source.
Whose actual image URL is https://i.imgur.com/04HZ5py.jpg
Similarly, on this topic https://howtodiscuss.com/t/how-to-do-handstand-yoga/28055
the image is actually hosted on this URL , u can see its source on my topic
So in all these cases i m facing 2 problems,
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These external images are not detected and shown as topic thumbnails in the topic preview plugin as u can see on my homepage right now https://howtodiscuss.com/ even though all my topics have images. but it doesn’t detect these images.
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Also, whenever i share my topics on social media sites like Facebook, Twitter, Linkedin or skype or anywhere, the meta OG tag doesn’t take my external img src and hence it falls back and always shows my site logo in the topic share link instead of the actual topic image that should be shown in social preview.
E.g see here on a facebook post, you can see that topic has indeed a topic picture but it still shows my site logo as fallback always 
You can put my URLs here to see the problem Social Share Preview of howtodiscuss.com - Social Share Preview – Check social media link previews
the topics have the images externally on public sites but it still always fallsback to my site logo. i do not want this behaviour.
My other friend is using Discourse and this topic list preview plugin also facing same problems @Bcat
How can i solve this? May be i can add a force meta OG tag on my topics HTML with the img src of the external CDN remote image? How do i do that? so that Social media sites and this topic list preview plugin can detect and show my topics images on my homepage.
Can you tell me how can i modify or overwrite the topic OG public tag for my each topic so that it must take those public images as topic thumbnails.?