WordPress snippet: Use Cloudinary JPGmini add-on to minify jpg site icons and jpg in content.

cloudinary-jpg-minify.php

<?php
add_filter( 'the_content', function ( $content ) {
	$doc = new DOMDocument();

	// modify state
	$libxml_previous_state = libxml_use_internal_errors( true );
	$doc->loadHTML( $content );
	// handle errors
	libxml_clear_errors();
	// restore
	libxml_use_internal_errors( $libxml_previous_state );

	$doc->preserveWhiteSpace = false;
	$images = $doc->getElementsByTagName( 'img' );
	$cloudinary_imgs = array();
	foreach ( $images as $img ) {
		$url = $img->getAttribute( 'src' );

		// if images is hosted at cloudinary
		if ( false !== stripos( $url, 'cloudinary' ) ) { 
			$cloudinary_imgs[] = $img;
		}
	}

	$remove_images = array();
	foreach ( $cloudinary_imgs as $cloudinary_image ) {
		$url = $cloudinary_image->getAttribute( 'src' );

		if ( '.jpg' === strrchr( $url, '.' ) ) {
			$cloudinary_image->setAttribute( 'src', convert_to_jpg_minfy( $url ) );
		}
	}
	return $doc->saveHTML();
}, 10, 1 );


add_filter( 'site_icon_meta_tags', function( $meta_tags ) {
	$minified_tags = array();
	foreach ($meta_tags as $metatag) {
		preg_match_all( '/href=\"([^\"]*)\"{1}/', $metatag, $matches );
		if ( isset( $matches[1][0] ) ) {
			$org_url = $matches[1][0];
			$minified_url = convert_to_jpg_minfy( str_replace( array( '.png', '.gif' ), '.jpg', $org_url) );
			$minified_tags[] = str_replace( $org_url, $minified_url, $metatag );
		}
	}
	return $minified_tags;
}, 10, 1 );


if (! class_exists( 'Cloudinary' ) ) {
	require_once  dirname( __FILE__ ) . '/cloudinary/Cloudinary.php'; // from https://github.com/cloudinary/cloudinary_php/tree/master/src
}
function convert_to_jpg_minfy( $url ) {
	try {
		\Cloudinary::config(array(
			'cloud_name' => 'CLOUDNAME',
			'api_key'    => 'API KEY',
			'api_secret' => 'API SECRET',
		));
		$url = cloudinary_url( basename( $url ) , array(
			'quality' => 'jpegmini',
			'sign_url' => true,
		) );
	} catch ( \Exception $e ) {
		write_log( $e->getMessage() );
	}
	return $url;
}

if ( ! function_exists( 'write_log' ) ) {
   function write_log( $log ) {
	   if ( is_array( $log ) || is_object( $log ) ) {
		   error_log( print_r( $log, true ) );
	   } else {
		   error_log( $log );
	   }
   }
}

Prerequisite, you've added the images using the Cloudinary WordPress plugin