Example PHP abstraction of an Image CDN. Built with CloudImage and an alias in mind, customise as your setup and provider.

1-usage.php

<?php

echo image([
  'image'   => 'otter.jpg',
  'alt'     => 'an otter standing on a log looking majestic',
  'srcset'  => [300, 450, 600, 800, 1000, 1200],
  'sizes'   => '100vw',
  'width'   => 1200,
  'height'  => 800,
  'loading' => 'lazy',
  'class'   => 'image-class'
]);

2-image.php

<?php

define( 'CDN_BASE', 'https://example.imagecdn.com' );

function image ( $args = [] ) {
  if (
    !$args['image'] ||
    !$args['width'] ||
    !$args['height']
  ) {
    return;
  }

  // set defaults here
  $defaults = [
    'alt'           => '',
    'srcset'        => [ 300, 450, 600, 800, 1000, 1200 ],
    'sizes'         => '(min-width: 82rem) 80rem, calc(100vw - 2rem)',
    'loading'       => 'lazy',
    'class'         => false,
    'picClass'      => false,
    'lowdpiQuality' => 80,
    'hidpiQuality'  => 40
  ];
  $opts = array_merge( $defaults, $args );
  
  $src = '/cdn/' . $args['image'];

  $fallback = create_src(
    $src,
    $opts['srcset'][count($opts['srcset']) - 1],
    $opts['lowdpiQuality']
  );
  $srcset = create_srcset( $src, $opts['srcset'], $opts['lowdpiQuality'] );
  $hidpi_srcset = create_srcset( $src, $opts['srcset'], $opts['hidpiQuality'] );

  $markup = sprintf(
    '<picture %s>
      <source media="(-webkit-min-device-pixel-ratio: 1.5)" srcset="%s" sizes="%s">
      <img %s alt="%s" src="%s" srcset="%s" sizes="%s" width="%s" height="%s" loading="%s" decoding="async">
    </picture>',
    $opts['picClass'] ? ('class="' . $opts['picClass'] . '"') : '',
    $hidpi_srcset,
    $opts['sizes'],
    $opts['class'] ? ('class="' . $opts['class'] . '"') : '',
    $opts['alt'],
    $fallback,
    $srcset,
    $opts['sizes'],
    $opts['width'],
    $opts['height'],
    $opts['loading']
  );

  return $markup;
}

// customise this function depending on your image CDN and setup
function create_src ( $path, $width, $quality ) {
  return CDN_BASE . $path . '?w=' . $width . '&q=' . $quality;
}

function create_srcset( $path, $widths, $quality ) {
  $srcset_arr = [];
  foreach ($widths as $width) {
    $url = create_src( $path, $width, $quality );
    $srcset_arr[] = $url . ' ' . $width . 'w';
  }

  return implode( ',', $srcset_arr );
}