Hide Full Width Image on Mobile Devices

Howdy,

I've done this with another theme, but can't get it to work with the theme I am using on this site.

I want to hide the full width image version on mobile devices and offer a cropped version instead (more of the lady, not just her shoes showing when viewed on mobile devices) on this page:

http://m24.siteground.biz/~websi541/joycebarwis.com/services/

Thanks in advance,
Casper