If you set your css to serve images at max-width: 100% they will resize themselves to fit any size. The browser will automatically resize them to fit the space they are in. BUT. You need to have a viewport setting metatag in the headers of your pages. Avoid fixed width settings for your block level elements, use % instead.

Page speed and mobile friendly design seem to be giving the edge to pages and sites where I have started switching things over to be one size fits all and you can get a good start in seeing what and how to make these changes at [developers.google.com...] where they offer a white paper .pdf download. There is a little learning, but the concepts for page building have shifted some and it is good to learn how to make it work for you.

The additional css code worked great N2. You're a genius.