So is this thumbnail when you share the forum in a chat for exemple. Normally it will show you the design or i don't know what exactly is with this thumbnail but for my forum the thumbnail is the old design that we had and i can't find the option to change it with the new design which appears when i share topics.
The first thumbnail is when i share the main page and the second thumbnail is when i share a topic page or a post. Does anybody how to change this?
I thought at first that it will change in time but 1-2 months passed from when i changed the design of the forum and nothing changed with that thumbnail...  
the forum : http://kureijiunit.onegoo.net/

What exactly do you mean by share?  Do you mean using the share buttons like Twitter, Facebook, etc?

Ok so... When you copy the main page forum URL and paste it to Skype (for ex.) that smile face appears as a thumbnail (design i think)
When i copy the URL from a post/thread and paste it to Skype (for ex.) the thumbnail is different, like in the first photo that i posted...
I want to have the second thumbnail for the main page too when i share the page not that creepy smile face .

Bump*
Nobody knows anything about this thing? ...

Bump*

I believe we had this similar issue with another share option (Facebook).  I believe it was stated that it can not be changed.