When I share some of my blog posts, Facebook doesn't display their right thumbail or anyn related image to the posts ... It just gives 3 unrelated thumbails to choose ...

For example , FB shows the right thumbail with this post :

http://www.moroccoenglish.com/?p=480

while it doesn't with this post :

http://www.moroccoenglish.com/?p=578

thanks for helping me ...

When I share some of my blog posts, Facebook doesn't display their right thumbail or anyn related image to the posts ... It just gives 3 unrelated thumbails to choose ...

For example , FB shows the right thumbail with this post :

http://www.moroccoenglish.com/?p=480

while it doesn't with this post :

http://www.moroccoenglish.com/?p=578

How can I set FB to display me the related thunmbails of the shared post ?

thanks for helping me ...