diff --git a/tests/phpunit/tests/media.php b/tests/phpunit/tests/media.php
index 90b7003..b26bd7e 100644
--- a/tests/phpunit/tests/media.php
+++ b/tests/phpunit/tests/media.php
@@ -52,7 +52,12 @@ function test_wp_lazy_load_content_media() {
 		$content_unfiltered = sprintf( $content, $img, $img_xhtml, $img_html5, $iframe, $img_eager );
 		$content_filtered   = sprintf( $content, $lazy_img, $lazy_img_xhtml, $lazy_img_html5, $iframe, $img_eager );
 
-		$this->assertSame( $content_filtered, wp_add_lazy_load_attributes( $content_unfiltered ) );
+		// Do not add srcset and sizes while testing.
+		add_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
+
+		$this->assertSame( $content_filtered, wp_filter_content_tags( $content_unfiltered ) );
+
+		remove_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
 	}
 
 	/**
@@ -70,11 +75,15 @@ function test_wp_lazy_load_content_media_opted_in() {
 		$content_unfiltered = sprintf( $content, $img );
 		$content_filtered   = sprintf( $content, $lazy_img );
 
+		// Do not add srcset and sizes while testing.
+		add_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
+
 		// Enable globally for all tags.
 		add_filter( 'wp_lazy_loading_enabled', '__return_true' );
 
-		$this->assertSame( $content_filtered, wp_add_lazy_load_attributes( $content_unfiltered ) );
+		$this->assertSame( $content_filtered, wp_filter_content_tags( $content_unfiltered ) );
 		remove_filter( 'wp_lazy_loading_enabled', '__return_true' );
+		remove_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
 	}
 
 	/**
@@ -88,10 +97,14 @@ function test_wp_lazy_load_content_media_opted_out() {
 			%1$s';
 		$content = sprintf( $content, $img );
 
+		// Do not add srcset and sizes while testing.
+		add_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
+
 		// Disable globally for all tags.
 		add_filter( 'wp_lazy_loading_enabled', '__return_false' );
 
-		$this->assertSame( $content, wp_add_lazy_load_attributes( $content ) );
+		$this->assertSame( $content, wp_filter_content_tags( $content ) );
 		remove_filter( 'wp_lazy_loading_enabled', '__return_false' );
+		remove_filter( 'wp_img_tag_add_srcset_and_sizes_attr', '__return_false' );
 	}
 }
diff --git a/wp-lazy-loading.php b/wp-lazy-loading.php
index 1eefea1..5c5c28b 100644
--- a/wp-lazy-loading.php
+++ b/wp-lazy-loading.php
@@ -31,14 +31,16 @@
  */
 function _wp_lazy_loading_initialize_filters() {
 	// The following filters would be merged into core.
-	foreach ( array( 'the_content', 'the_excerpt', 'comment_text', 'widget_text_content' ) as $filter ) {
-		// After parsing blocks and shortcodes.
-		add_filter( $filter, 'wp_add_lazy_load_attributes', 25 );
+	foreach ( array( 'the_content', 'the_excerpt', 'widget_text_content' ) as $filter ) {
+		add_filter( $filter, 'wp_filter_content_tags' );
 	}
 
 	// The following filters are only needed while this is a feature plugin.
 	add_filter( 'wp_get_attachment_image_attributes', '_wp_lazy_loading_add_attribute_to_attachment_image' );
 	add_filter( 'get_avatar', '_wp_lazy_loading_add_attribute_to_avatar' );
+
+	// The following relevant filter from core should be removed when merged.
+	remove_filter( 'the_content', 'wp_make_content_images_responsive' );
 }
 
 add_action( 'plugins_loaded', '_wp_lazy_loading_initialize_filters', 1 );
@@ -102,7 +104,7 @@ function _wp_lazy_loading_add_attribute_to_attachment_image( $attr ) {
  */
 function wp_lazy_loading_enabled( $tag_name, $context ) {
 	// By default add to all 'img' tags.
-	// See https://github.com/whatwg/html/issues/2806
+	// See https://html.spec.whatwg.org/multipage/embedded-content.html#attr-img-loading
 	$default = ( 'img' === $tag_name );
 
 	/**
@@ -118,57 +120,150 @@ function wp_lazy_loading_enabled( $tag_name, $context ) {
 }
 
 /**
- * Add `loading="lazy"` to `img` HTML tags.
+ * Filters specific tags in post content and modifies their markup.
  *
- * Currently the "loading" attribute is only supported for `img`, and is enabled by default.
+ * This function adds `srcset`, `sizes`, and `loading` attributes to `img` HTML tags.
  *
  * @since (TBD)
  *
+ * @see wp_img_tag_add_loading_attr()
+ * @see wp_img_tag_add_srcset_and_sizes_attr()
+ *
  * @param string $content The HTML content to be filtered.
  * @param string $context Optional. Additional context to pass to the filters. Defaults to `current_filter()` when not set.
- * @return string Converted content with 'loading' attributes added to images.
+ * @return string Converted content with images modified.
  */
-function wp_add_lazy_load_attributes( $content, $context = null ) {
+function wp_filter_content_tags( $content, $context = null ) {
 	if ( null === $context ) {
 		$context = current_filter();
 	}
 
-	if ( ! wp_lazy_loading_enabled( 'img', $context ) ) {
+	$add_loading_attr = wp_lazy_loading_enabled( 'img', $context );
+
+	if ( false === strpos( $content, '<img' ) ) {
 		return $content;
 	}
 
-	return preg_replace_callback(
-		'/<img\s[^>]+>/',
-		function( array $matches ) use( $content, $context ) {
-			if ( ! preg_match( '/\sloading\s*=/', $matches[0] ) ) {
-				$tag_html = $matches[0];
-
-				/**
-				 * Filters the `loading` attribute value. Default `lazy`.
-				 *
-				 * Returning `false` or an empty string will not add the attribute.
-				 * Returning `true` will add the default value.
-				 *
-				 * @since (TBD)
-				 *
-				 * @param string $default The filtered value, defaults to `lazy`.
-				 * @param string $tag_html The tag's HTML.
-				 * @param string $content The HTML containing the image tag.
-				 * @param string $context Optional. Additional context. Defaults to `current_filter()`.
-				 */
-				$value = apply_filters( 'wp_set_image_loading_attr', 'lazy', $tag_html, $content, $context );
+	if ( ! preg_match_all( '/<img\s[^>]+>/', $content, $matches ) ) {
+		return $content;
+	}
+
+	// List of the unique `img` tags found in $content.
+	$images = array();
 
-				if ( $value ) {
-					if ( ! in_array( $value, array( 'lazy', 'eager' ), true ) ) {
-						$value = 'lazy';
-					}
+	foreach ( $matches[0] as $image ) {
+		if ( preg_match( '/wp-image-([0-9]+)/i', $image, $class_id ) ) {
+			$attachment_id = absint( $class_id[1] );
 
-					return str_replace( '<img', '<img loading="' . $value . '"', $tag_html );
-				}
+			if ( $attachment_id ) {
+				/*
+				 * If exactly the same image tag is used more than once, overwrite it.
+				 * All identical tags will be replaced later with 'str_replace()'.
+				 */
+				$images[ $image ] = $attachment_id;
+				continue;
 			}
+		}
+
+		$images[ $image ] = 0;
+	}
+
+	// Reduce the array to unique attachment IDs.
+	$attachment_ids = array_unique( array_filter( array_values( $images ) ) );
+
+	if ( count( $attachment_ids ) > 1 ) {
+		/*
+		 * Warm the object cache with post and meta information for all found
+		 * images to avoid making individual database calls.
+		 */
+		_prime_post_caches( $attachment_ids, false, true );
+	}
+
+	foreach ( $images as $image => $attachment_id ) {
+		$filtered_image = $image;
+
+		// Add 'srcset' and 'sizes' attributes if applicable.
+		if ( $attachment_id > 0 && false === strpos( $filtered_image, ' srcset=' ) ) {
+			$filtered_image = wp_img_tag_add_srcset_and_sizes_attr( $filtered_image, $context, $attachment_id );
+		}
+
+		// Add 'loading' attribute if applicable.
+		if ( $add_loading_attr && false === strpos( $filtered_image, ' loading=' ) ) {
+			$filtered_image = wp_img_tag_add_loading_attr( $filtered_image, $context );
+		}
+
+		if ( $filtered_image !== $image ) {
+			$content = str_replace( $image, $filtered_image, $content );
+		}
+	}
+
+	return $content;
+}
+
+/**
+ * Adds `loading` attribute to an existing `img` HTML tag.
+ *
+ * @since (TBD)
+ *
+ * @param string $image   The HTML `img` tag where the attribute should be added.
+ * @param string $context Additional context to pass to the filters.
+ * @return string Converted `img` tag with `loading` attribute added.
+ */
+function wp_img_tag_add_loading_attr( $image, $context ) {
+	/**
+	 * Filters the `loading` attribute value. Default `lazy`.
+	 *
+	 * Returning `false` or an empty string will not add the attribute.
+	 * Returning `true` will add the default value.
+	 *
+	 * @since (TBD)
+	 *
+	 * @param string $value   The 'loading' attribute value, defaults to `lazy`.
+	 * @param string $image   The HTML 'img' element to be filtered.
+	 * @param string $context Additional context about how the function was called or where the img tag is.
+	 */
+	$value = apply_filters( 'wp_img_tag_add_loading_attr', 'lazy', $image, $context );
+
+	if ( $value ) {
+		if ( ! in_array( $value, array( 'lazy', 'eager' ), true ) ) {
+			$value = 'lazy';
+		}
+
+		return str_replace( '<img', '<img loading="' . $value . '"', $image );
+	}
+
+	return $image;
+}
+
+/**
+ * Adds `srcset` and `sizes` attributes to an existing `img` HTML tag.
+ *
+ * @since (TBD)
+ *
+ * @param string $image         The HTML `img` tag where the attribute should be added.
+ * @param string $context       Additional context to pass to the filters.
+ * @param int    $attachment_id Image attachment ID.
+ * @return string Converted 'img' element with 'loading' attribute added.
+ */
+function wp_img_tag_add_srcset_and_sizes_attr( $image, $context, $attachment_id ) {
+	/**
+	 * Filters whether to add the `srcset` and `sizes` HTML attributes to the img tag. Default `true`.
+	 *
+	 * Returning anything else than `true` will not add the attributes.
+	 *
+	 * @since (TBD)
+	 *
+	 * @param bool   $value         The filtered value, defaults to `true`.
+	 * @param string $image         The HTML `img` tag where the attribute should be added.
+	 * @param string $context       Additional context about how the function was called or where the img tag is.
+	 * @param int    $attachment_id The image attachment ID.
+	 */
+	$add = apply_filters( 'wp_img_tag_add_srcset_and_sizes_attr', true, $image, $context, $attachment_id );
+
+	if ( true === $add ) {
+		$image_meta = wp_get_attachment_metadata( $attachment_id );
+		return wp_image_add_srcset_and_sizes( $image, $image_meta, $attachment_id );
+	}
 
-			return $matches[0];
-		},
-		$content
-	);
+	return $image;
 }