$userID = 'мой ид';
$secret = $_REQUEST['secret'];
$sid = $_REQUEST['sid'];
//формеруем сигнатуру
$sig = md5($userID."api_id=ИД_ПРИЛОЖЕНИЯfields=photoformat=JSONmethod=getProfilesuids=".$userID."v=3.0$secret");
//отправляем запрос
$req = "http://api.vkontakte.ru/api.php?api_id=ИД_ПРИЛОЖЕНИЯ&fields=photo&format=JSON&method=getProfiles&uids=".$userID."&v=3.0&sid=".$sid."&sig=".$sig;
//выполняем запрос
echo urldecode(stripcslashes(file_get_contents($req)));
ответ
{"error":{"error_code":4,"error_msg":"Incorrect signature","request_params":[{"key":"api_id","value":"хххх"},{"key":"fields","value":"photo"},{"key":"format","value":"JSON"},{"key":"method","value":"getProfiles"},{"key":"uids","value":"ххххх"},{"key":"v","value":"3.0"},{"key":"sid","value":"87403b64c1b61c7cfd8fe95d65641a8e350e5f4a6f6a699e52393dff10"},{"key":"sig","value":"6b9c8eed6dc04684a0fe003ae5cec1ab"}]}}