Content automatically resizing

Every image I put into a post automatically stretches to fit the width of the entire post area. If anyone could point me in the direction of the code area that would be causing this I would greatly appreciate it. I assume I have a 100% width somewhere making all of the content stretch but i’m not really sure where that would be.
I am using the twenty-eleven theme if that information is needed. If any code is needed I can post that as well.