[Commentor] LC-415 Charles McCathieNevile on behalf of Opera Software [Working Group decision] We have clarified that only images with an intrinsic size should have their dimensions specified in the markup. [Commentor reply] yes [Comment] 
There are some types of image, such as SVG, where a pixel-based size is unnecessary or inappropriate. In such cases it is often appropriate to use CSS to specify width/height rather than HTML attributes. cheers Chaals