Both the width, height, and style attributes are valid in HTML5.
However, we suggest using the style attribute. It prevents internal or external styles
sheets from changing the original size of images:
Example
<!DOCTYPE html>
<html>
<head>
<style>
img {
width:100%; }</style>
</head>
<body>
<img src="html5.gif" alt="HTML5 Icon" style="width:128px;height:128px;">
<img src="html5.gif" alt="HTML5 Icon" width="128" height="128">
</body>
</html>
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