Remove Width and Height Attributes from Images

When you upload an image using WordPress media and then insert it into the content editor, the image is attached with width and height attributes. These attributes are generally desirable because they help the browser reserve the right space for the image during layout.

But if you want to prevent WordPress from adding these width and height attributes, add the following code to your theme’s functions.php file:

add_filter( 'post_thumbnail_html', 'remove_width_attribute', 10 );
add_filter( 'image_send_to_editor', 'remove_width_attribute', 10 );

function remove_width_attribute( $html ) {
   $html = preg_replace( '/(width|height)="d*"s/', "", $html );
   return $html;
}