PHP: WordPress remove width and height from image tags for responsive images

gistfile1.txt

/**
* Removes width and height attributes from image tags
*
* @param string $html
*
* @return string
*/
function remove_image_size_attributes( $html ) {
return preg_replace( '/(width|height)="\d*"/', '', $html );
}
 
// Remove image size attributes from post thumbnails
add_filter( 'post_thumbnail_html', 'remove_image_size_attributes' );
 
// Remove image size attributes from images added to a WordPress post
add_filter( 'image_send_to_editor', 'remove_image_size_attributes' );