Do not want rounded corners for some images

Firstly, I would like to apologise if this is against the rules as I have two problematic threads going. I wasn't sure how to go about this as I didn't see rules in regards to it. I have two separate problems so I just assumed to create two separate threads. Please correct me if I'm wrong.

Anywho, the images on my forum have been set to have rounded corners, however, there are some images that I do not wish to have rounded corners. There are only a few that I do not wish to have rounded corners and I am wondering if there is some code, or something i can add to the specific image code to have straight corners instead?

My forum is PHPBB2 and the link is www.tester.omgforum.net

Which images are you not wanting to have rounded corners?  You currently have it on maintenance, so at the moment, I can't see much.

Sorry @Leah7 , I've switched the maintenance mode off.

On the portal page I would like the Admin images without rounded corners, and also on the main forum page, the compass - I do not want this rounded either.