They seem to be missing the “image” tag. I’ve noticed the same error for many sites I try and onebox (usually the more amateur ones), but we really should have this sorted ‘in house’!
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It does onebox just fine, I believe the only “bug” is that the message is wrong:
Sorry, we were unable to
generate a preview for this web page, because the following oEmbed / OpenGraph tag could not be found: image
should be
Sorry, we were unable to get an image for this web page preview, because the following oEmbed / OpenGraph tag could not be found: image.
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Thanks Rafael - yes it does onebox okay. Why can’t it get the image?
Because the target page doesn’t have the necessary tag, which is literally what the error tells you:
because the following oEmbed / OpenGraph tag could not be found: image
Our blog is Wordpress, and it doesn’t have the image tag setup for this post.
I don’t see how this is a bug on Discourse 
Ah - I foolishly assumed that you used the Discourse published pages feature for your blog.
Is the image tag on your Wordpress site unfixable? Because it looks a bit silly to have that error in a Discourse onebox to a discourse.org blog!
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We’re in the process of switching away from WordPress to a static HTML solution for the blog, so this can be improved when that is rolled out.
Any opinion on this @jamie.wilson ? Is this something we can improve?
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@falco’s suggested text is good for cases where we’re only missing an image tag:
Sorry, we were unable to get an image for this web page preview, because the following oEmbed / OpenGraph tag could not be found: image.
Or perhaps we just treat cases of only missing an image tag as a non-failure, and display no message at all?
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Yeah, let’s do that! 
If the only thing missing is the image tag, that’s not really a problem any more since we have enough to generate a decent preview. And if someone is thinking “hmm why isn’t there an image in this onebox” they don’t need a nudge, as the next investigative steps are obvious: look for the image tag!
Can you make it so?
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https://github.com/discourse/discourse/pull/12216
Has been merged in.
A preview now looks like this:
(Previews can be cached for up to 24 hours. So if you’re testing you may find you get the missing image error message. If so, throw some extra query params on the end of the URL to make it bypass the cache and generate a fresh preview.)
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