I have some urls like this one
http://www.d10scup.com/notizia/122/
with og meta tags in it as you can see here on the fb linter
http://developers.facebook.com/tools/debug/og/object?q=http%3A%2F%2Fwww.d10scup.com%2Fnotizia%2F122%2F
The problem is that when you copy/paste this url on facebook it shows the wrong image. I really don't understand what the problem might be since the debugger doesn't give any unexpected result.
Hope someone can help me.
I think that og:image works well when the user likes the page. In case of share, FB parses the images from the page and the user is shown options.
I would suggest you to try 2 things: 1) Use more than 1 og:image tags and see what comes up. 2) Use the correct image as the last image in the page and set that to hidden. Maybe FB will parse that and will show that as the first image.