partial solution to WP responsive images

shc_responsive_images.php

<?php
/*
 * full version of code I added in a comment on wpscholar.com about how
 * make it easier for WP to produce responsive images
 * @link https://wpscholar.com/blog/remove-wp-image-size-attributes/#comment-23731
 *
 * Note: I make no claims that this handles all cases, just those problems
 * 		 identified by others commenting on the OP's code
 */

// 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', 21 );

// Tell the [caption] shortcode not to output a "style: width: xxxpx" HTML attribute
add_filter( 'img_caption_shortcode_width', '__return_false' );

/**
 * Removes width and height attributes from image tags
 *
 * @param string $html
 * @return string
*/
function remove_image_size_attributes( $html ) {
	// Find the <img> tag (so that we don't strip width from a [caption] shortcode)
	preg_match_all( '!<img [^>]+>!i', $html, $matches, PREG_SET_ORDER );
	if ( ! empty( $matches ) ) {
		$html = str_replace( $matches[0][0], preg_replace( '/(width|height)="\d*" /', '', $matches[0][0] ), $html );
	}

	return $html;
}

/**
 * Tell the [caption] shortcode not to output a "style: width: xxxpx" HTML attribute
 *
 * @param string $html
 * @return string
*/
function img_caption_shortcode_width() {
	return 0;
}