diff --git a/include/webdav_image_runtime.inc.php b/include/webdav_image_runtime.inc.php
index f1ef201..80e58da 100644
--- a/include/webdav_image_runtime.inc.php
+++ b/include/webdav_image_runtime.inc.php
@@ -11,7 +11,7 @@ function bratonien_tools_webdav_image_source_info($image_id)
   if ($image_id < 1) return null;
   if (array_key_exists($image_id, $cache)) return $cache[$image_id];
 
-  $result = pwg_query('SELECT path FROM '.IMAGES_TABLE.' WHERE id='.$image_id.' LIMIT 1');
+  $result = pwg_query('SELECT path, coi FROM '.IMAGES_TABLE.' WHERE id='.$image_id.' LIMIT 1');
   if (!pwg_db_num_rows($result)) return $cache[$image_id] = null;
   $row = pwg_db_fetch_assoc($result);
   $path = (string)($row['path'] ?? '');
@@ -94,6 +94,7 @@ function bratonien_tools_webdav_image_source_info($image_id)
     'content_type'=>$content_type,
     'size'=>$size,
     'etag'=>$etag,
+    'coi'=>$row['coi'] ?? null,
   );
 }
 
@@ -116,6 +117,121 @@ function bratonien_tools_webdav_preview_path(array $info)
   return is_file($path) && is_readable($path) ? $path : null;
 }
 
+function bratonien_tools_webdav_custom_derivative_params($key)
+{
+  if (!class_exists('DerivativeParams') || !class_exists('SizingParams')) return null;
+  $tokens = explode('_', (string)$key);
+  if (!$tokens) return null;
+
+  $token = array_shift($tokens);
+  $crop = 0;
+  $min_size = null;
+  $parse_size = function($value)
+  {
+    $parts = explode('x', (string)$value, 2);
+    if (count($parts) === 1)
+    {
+      $size = max(1, (int)$parts[0]);
+      return array($size, $size);
+    }
+    return array(max(1, (int)$parts[0]), max(1, (int)$parts[1]));
+  };
+
+  if (isset($token[0]) && $token[0] === 's')
+  {
+    $size = $parse_size(substr($token, 1));
+  }
+  elseif (isset($token[0]) && $token[0] === 'e')
+  {
+    $crop = 1;
+    $size = $min_size = $parse_size(substr($token, 1));
+  }
+  else
+  {
+    if (count($tokens) < 2) return null;
+    $size = $parse_size($token);
+    $crop_token = array_shift($tokens);
+    $min_size = $parse_size(array_shift($tokens));
+    $crop = function_exists('char_to_fraction') ? char_to_fraction($crop_token) : 0;
+  }
+
+  $params = new DerivativeParams(new SizingParams($size, $crop, $min_size));
+  if (class_exists('ImageStdParams')) ImageStdParams::apply_global($params);
+  return $params;
+}
+
+function bratonien_tools_webdav_derivative_variants()
+{
+  $variants = array();
+  if (!class_exists('ImageStdParams')) return $variants;
+
+  foreach (ImageStdParams::get_defined_type_map() as $type => $params)
+  {
+    $variants['standard:'.$type] = $params;
+  }
+  foreach (ImageStdParams::$custom as $custom_key => $last_used)
+  {
+    $params = bratonien_tools_webdav_custom_derivative_params($custom_key);
+    if ($params) $variants['custom:'.$custom_key] = $params;
+  }
+  return $variants;
+}
+
+function bratonien_tools_webdav_generate_derivative($params, $src_image)
+{
+  if (!is_object($src_image) || empty($src_image->id)) return false;
+  $info = bratonien_tools_webdav_image_source_info((int)$src_image->id);
+  if (!$info) return false;
+  $preview = bratonien_tools_webdav_preview_path($info);
+  if (!$preview) return false;
+
+  if (!class_exists('DerivativeImage')) require_once(PHPWG_ROOT_PATH.'include/derivative.inc.php');
+  if (!class_exists('pwg_image')) require_once(PHPWG_ROOT_PATH.'admin/include/image.class.php');
+
+  $derivative = new DerivativeImage($params, $src_image);
+  $target = $derivative->get_path();
+  if ($target === '' || strpos($target, PHPWG_ROOT_PATH.PWG_DERIVATIVE_DIR) !== 0) return false;
+
+  $preview_mtime = @filemtime($preview) ?: 0;
+  if (is_file($target) && is_readable($target) && (@filemtime($target) ?: 0) >= $preview_mtime)
+  {
+    return true;
+  }
+
+  $directory = dirname($target);
+  if (!is_dir($directory) && !mkdir($directory, 0755, true) && !is_dir($directory)) return false;
+
+  $image = new pwg_image($preview);
+  try
+  {
+    $original_size = array($image->get_width(), $image->get_height());
+    $crop_rect = null;
+    $scaled_size = null;
+    $params->sizing->compute($original_size, $info['coi'] ?? null, $crop_rect, $scaled_size);
+    if ($crop_rect)
+    {
+      $image->crop($crop_rect->width(), $crop_rect->height(), $crop_rect->l, $crop_rect->t);
+    }
+    if ($scaled_size)
+    {
+      $image->resize($scaled_size[0], $scaled_size[1]);
+    }
+    if (!empty($params->sharpen))
+    {
+      $image->sharpen($params->sharpen);
+    }
+    $image->write($target);
+  }
+  finally
+  {
+    $image->destroy();
+  }
+
+  @chmod($target, 0644);
+  clearstatcache(true, $target);
+  return is_file($target) && is_readable($target);
+}
+
 function bratonien_tools_filter_webdav_src_url($url, $src_image)
 {
   if (!is_object($src_image) || empty($src_image->id)) return $url;
@@ -126,6 +242,25 @@ function bratonien_tools_filter_webdav_src_url($url, $src_image)
 function bratonien_tools_filter_webdav_derivative_url($url, $params, $src_image, $rel_url)
 {
   if (!is_object($src_image) || empty($src_image->id)) return $url;
+  $info = bratonien_tools_webdav_image_source_info((int)$src_image->id);
+  if (!$info) return $url;
+
+  try
+  {
+    if (bratonien_tools_webdav_generate_derivative($params, $src_image))
+    {
+      // Keep Piwigo's normal derivative URL. The file behind it now contains
+      // the derivative generated from the prepared WebDAV preview.
+      return $url;
+    }
+  }
+  catch (Throwable $e)
+  {
+    error_log('Bratonien WebDAV derivative #'.(int)$src_image->id.': '.$e->getMessage());
+  }
+
+  // Last-resort display fallback: show the prepared preview/original stream
+  // instead of allowing Piwigo to derive from the 1x1 placeholder.
   $webdav_url = bratonien_tools_webdav_image_url((int)$src_image->id, true);
   return $webdav_url ?: $url;
 }