resizing IMG on HTML page with css

I am displaying an IMG inside HTML.

The SRC attribute is dynamic and can point to different image each time.

I want to restrict the size of the image displayed to 200x200 PX maximum. So if the image was bigger then it will resize its biggest dimension to 200, respecting its dimension ratio. And if both dimensions smaller than 200 then keep as it is. Is there to do that with CSS only without JavaScript?