Featured image

Hello!
I’ve read the other threads about the width of featured image, but I’m having another problem.

I used an image of 1200px of width, but still, the image doesn’t extend to the whole content area width.
Here’s the address : http://www.lookforthesparks.com/

I can’t find where the problem comes from.
And I have the same issue with images even wider than 1200px.

Thanks in advance for the help! 🙂