Задача: добавить watermark на товары импортируемые из 1С.
Откроем result_modifier.php в catalog.element, catalog.sections и добавим функцию:

$arWatermark = Array(
	array(
		"name" => "watermark", 
		"position" => "center", 
		"size" => "real", 
		"type" => "image", 
		"alpha_level" => 50,
		"file" => $_SERVER['DOCUMENT_ROOT']."/img/watermark.png"
	)
);

Теперь при вызове функции ResizeImageGet нужно добавить наш водяной знак:

if ($arResult['DETAIL_PICTURE']['SRC']) {
$big_file = CFile::ResizeImageGet($arResult['DETAIL_PICTURE']['ID'], array('width' => 2000, 'height' => 2000), BX_RESIZE_IMAGE_PROPORTIONAL, true, $arWatermark);
$arResult['DETAIL_PICTURE']['SRC'] = $big_file['src'];