Hi webmasters, so many of us respect old rules of providing images with alt and also WIDTH - HEIGHT attributes, it helps to display the content as it loads and it's been considered important for validation.
But... responsive design means images, while being the same img-file, can have diff widths and height depending on your window size or device. If you remove those attributes (width and height) the design still works based on CSS, but the html won't validate. How important do you think is this? We have lots of old threads regarding how search engines value our websites, validation has been considered by many as "good", valuable point.
Would you keep or remove the width and height on your images? even that CSS would make this obsolete while rendering (unless the css file hasn't been loaded).