Different header image for browser and devices

Hello,

I have a child theme which I have been customizing to my needs. Some time ago I changed my header image (you can see it here http://acuhealth.org.uk/) and afterwards I realised that it didn’t really work on IE and that it couldn’t be read on mobile devices.

I think it’s on I.E. that the image gets cropped and as mentioned, text can’t be seen on a mobile so I’d like to:

– Amend the dimension of my image so it’s seen ok in all browsers. Is there a way to specify sizes for each browser?
– Change completely my image (without text or link) for mobile devices

Any help would be much appreciated!

Thanks in advance, Alexandra