image-render.php

<?php
require_once './vendor/autoload.php';
$client = new Sanity\Client([
  'projectId' => '3do82whm',
  'dataset' => 'production',
  'useCdn' => true,
]);

$doc = $client->getDocument('47abbe60-f184-4eff-99e0-3a85c5c07c3a');
$html = Sanity\BlockContent::toHtml($doc['body'], [
  'serializers' => [
    'image' => function ($node) use ($client) {
      $image = $client->getDocument($node['attributes']['asset']['_ref']);
      $url = $image['url'] . '?w=640';
      return '<img src="' . $url . '">';
    }
  ]
]);

echo $html;