I just published a new website. When someone tries to publish the link on Facebook, no thumbnail-options shows up, even though there are plenty of image-files to choose from.
When I post the link to the “gallery” section though, I get the option to choose a thumbnail from the images in the gallery only.
The url to the website: http://www.ridderhest.no
According to the debug tool: https://developers.facebook.com/tools/debug/og/object?q=http%3A%2F%2Fwww.ridderhest.no the image is being detected correctly from your tags and it appears to meet the size requirements, does it work it you change the image to be slightly larger? the minimum supported size is 50×50 and that’s exactly the size of the image, maybe a 51×51 image works?