50cool50 on "[Plugin: Jetpack by WordPress.com] Viewing Compressed theme on Tablet - Loosing HEader Image from site"

Hi
I installed Jetpack a few moments ago to get my theme to respond better on a mobile device. The theme looks and respnds better, but I am loosing my header image.
Is there any way to get back my header or, is there any way to install another image that will only load when viewed on a mobile device but is hidden when viewed on a large PC?
Apologies for my noob limited tech language

http://wordpress.org/plugins/jetpack/