Background Image not Responsive

I have a website I just created with arcade theme, but it is not up yet. Below is a screen shot of it and will try to explain the situation as best I can.

http://i57.tinypic.com/2nls1ex.png

When I view my website on different screen resolutions the site works and views fine no problem. The only issue is that the background photo of the cow on the right side of the screen, the cows face is not on the screen, his head is off from the background. This only happens when viewing the website any lower then 1024 x 600 resolution. So for tablets and mobile devices you won’t be able to see the cows face.

To make the background full screen, I had to add FullBack 1.1 by WPMule plugin.

How can I make the cows face alway show in the background when viewing the site on any resolution and devices? Thank you.