You need to check your settings, I believe you will find the answer there.
Go to the blue bar at the top of the page:
Forum Actions, General Settings
A little bit down the page is a section titled Thread Display Options
Click to checkmark the elements that you want displayed
Show Signatures
Show Avatars
Show Images
I'm thinking that the Show Images box is the one that may be causing you to only see thumbprints instead of the entire picture. Hope this helps.