Window image Resize issues

Hello

I have made a custom theme based off of the twenty eleven theme, I now have trouble with some images not resizing automatically when the window is resized.

The address is: http://www.lisalaw.co.nz

I would like to know why the banner image and the main page slide show does not want to resize with the other elements in the web site! Please could someone help.

You will know what i am talking about if you open the website and start resizing the window below 1024×768, it becomes a mess.