when you try to share a link on a fan page, some times use the image from meta og:image but some times uses a random image.
site is: http://maite.com.br/blog/
metas i'm using:
<meta property="og:image" content="http://maite.com.br/blog/imagens/posts/face_icon.jpg"/>
<meta property="og:url" content="http://maite.com.br/blog/"/>
<meta property="og:type" content="blog"/>
<meta property="og:tittle" content="Maite Proença Blog"/>
i have had this same problem . when i shared some thing on face book it doesn't show as the same featured image on my website: my site: http://www.technobezz.com/
If you are using wordpress please try these plugin's from wordpress because it worked for me and others
http://wordpress.org/plugins/facebook-featured-image-and-open-graph-meta-tags/
thanks