downloadImageFromUrl.php

<?php

  function downloadImageFromUrl($url) {
    $ch = curl_init();

    curl_setopt($ch, CURLOPT_URL, $url);
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);

    $result = curl_exec($ch);
    $contentType = curl_getinfo($ch, CURLINFO_CONTENT_TYPE);
    
    if (curl_errno($ch)) {
      // do whatever you want with the error
      $error = curl_error($ch);
      $result = false;
    }

    if (empty($contentType) || strpos($contentType, 'image') === false) {
      $result = false;
    }
    
    curl_close($ch);
    
    return [
      'result' => $result,
      'contentType' => $contentType
    ];
  }

  function getExtensionFromMime($mime) {
    if (!is_string($mime) || strpos($mime, '/') === false) return false;

    return explode('/', $mime)[1];
  }

  // if you run this function (usageExample) you will download the unsplash
  // image on $url on your current directory with the name downloaded_image.jpg

  function usageExample() {
    $url = 'https://images.unsplash.com/photo-1606787620484-4561d4d20907';
    $remote_image_data = downloadImageFromUrl($url);
    
    if (!empty($remote_image_data['result'])) {
      $image_data = $remote_image_data['result'];
      $image_ext = getExtensionFromMime($remote_image_data['contentType']);
      $image_dest = __DIR__ . '/downloaded_image' . '.' . $ext;

      file_put_contents($image_dest, $image_data);
    }
  }