Wordpress images

I have a problem with the images on a website that I am working on. It's difficult to explain so I try to show you instead.

Step 1. go to http://www.cierrafitness.com

step 2. hold control while using the scroll wheel on your mouse to change the size of your screen.

You will see the images start to move and overlap each other... Please give me some advise to correct this problem.

Thanks.