copyPhotos

\Bitrix\Main\Loader::includeModule('iblock');
$iblockId = 20;
$propPhoto = 'MORE_PHOTO';
$propArt = 'CML2_ARTICLE';
$dirName = 'PHOTO_FOR_IBLOCK_' . $iblockId;

$arSelect = [
    'ID', 'IBLOCK_ID',
    'PROPERTY_' . $propArt,
    'DETAIL_PICTURE',
    'PREVIEW_PICTURE'
];

$db = CIblockElement::GetList([], ['IBLOCK_ID' => $iblockId], false ,false, $arSelect);
$arEls = [];
while($ob = $db->GetNext()){
    $dbProp = CIBlockElement::GetProperty($iblockId, $ob['ID'], "sort", "asc", array("CODE" => $propPhoto));
    $propVals = [];

    if(!empty($ob['PREVIEW_PICTURE'])) $propVals[] = $ob['PREVIEW_PICTURE'];
    if(!empty($ob['DETAIL_PICTURE'])) $propVals[] = $ob['DETAIL_PICTURE'];

    while ($obProp = $dbProp->GetNext()){
        $propVals[] = $obProp['VALUE'];
    }

    if(count($propVals) == 1 && (int)current($propVals) == 0)
        $propVals = [];

    if(count($propVals) > 0)
        $arEls[$ob['PROPERTY_' . $propArt . '_VALUE']] = $propVals;
}

$baseDir = $_SERVER['DOCUMENT_ROOT'] . '/upload/' . $dirName . '/';
if(!is_dir($baseDir)) mkdir($baseDir, 0777, true);

foreach($arEls as $art => $photos){
    $dirItem = $baseDir . $art . '/';
    if(!is_dir($dirItem)) mkdir($dirItem, 0777, true);

    foreach($photos as $key => $photoId){
        $path = $_SERVER['DOCUMENT_ROOT'] . CFile::GetPath($photoId);
        $type = array_pop(explode('.', $path));
        copy($path, $dirItem . $key . '.' . $type);
    }
}