2. Then noticed that it wants the open graph og:url and also mention semething wrong with og:image such as “Provided og:image is not big enough. Please use an image that’s at least 200×200 px.”. I am very sure the image is more than 200×200.
3. I changed og:image from jpg to png.
4. Then add parameter to xxx.png?a=b (just a dummy parameter so that FB will re-cache).
Then I got the right image shows up in the share dialogue box. Hope this help you too.