said 1 year, 1 month ago:
OK, after a bit of testing I think I have it figured out. Facebook does indeed seem to have a preference for one image format over another, in this order
So, I think you might get great results by making sure that:
1) if you have more than one jpg on the page, make sure you have the one you want Facebook to use earliest on the page
2) if you have any other images on the page, make sure the one you want Facebook to use is in jpg format, because if it’s a gif and at the top, Facebook will pull the first jpg it finds (or png if there are no jpg’s).
OK, I hope I explained that well! :)
The reason the the WP.com OG tags don’t solve the problem is because WP.com lists *all* your images in your OG tags, so that still leaves FB to choose which one it wants. If you had total control over your OG tags, and could set *only one* image in your OG tags, I believe then FB would not look for any other images not matter what format your designated image was in.