I have created a site jimart.co.uk, using a responsive template.

The thumbnail pictures work fine in tablet or smartphone mode, but in the desktop mode many appear as anything but thumbails.

as an example http://jimart.co.uk/iris.html only 1 picture is the correct size.

I have checked the original images and they are the correct size when you check their properties, but not when they display.

can anyone tell me what I maybe doing wrong? or suggest a solution

Thanks