How to update the image (preview_image) when updating or adding an infoblock element?

Question

1C-Bitrix

How can I apply my own code to a loaded image when updating or adding an infoblock element?

I'm trying to do it via AddEventHandler()

AddEventHandler('iblock', 'OnAfterIBlockElementUpdate', array('MyClass',  'OnAfterIBlockElementHandler'));
// ...

public function OnAfterIBlockElementHandler(&$arFields)
{
    print_r($arFields['PREVIEW_PICTURE']);
}

but only the ID of the old picture is shown there, and the new picture is not available

Array (
    [name] => Имя_файла.jpg
    [type] => image/jpeg
    [tmp_name] => /path/temp/620/default
    [size] => 74463
    [error] => 0
    [description] =>
    [COPY_FILE] => Y
    [copy] => 1
    [MODULE_ID] => iblock
    [old_file] => 473084
)