Images displaying beyond original scale

Hello there,

I’m having a problem figuring out the source of an image display issue. I’m using a custom template (based on Bones). When I insert an image into a post or a page something is overriding the proportions of the original image and stretching it out to the full width of the post/page.
So, for example, if I insert an image that is 200×200 when I preview the result it’s massive (and, no surprise, ugly).
At first I thought that WP may be putting in something into the code of the image link, but even when I strip the code down to just the image-source itself I end up with the same result.

Where should I look for where the override may be? One thing I’ll note is that images used in the header do not suffer from this problem.

Thanks.