Image optimization for responsive site

Hi,

I am trying to ensure that our website is running at optimum speed, but when running it through the google page speed insights, I get a lot of warnings over image size and optimization. I assume that this is to do with the fact that, rather than separate mobile and desktop sites, I am using a responsive theme, but is there a good way of sorting this to speed up mobile load times?

The website is here http://www.yorkshirevets.co.uk so if there is any other obvious reason for this problem, and it’s not a responsive theme issue, please let me know.

Thanks