function check_empty_string($string) {
            $string = trim($string);
            if (empty($string)) {
                return '%';
            }
            return $string . '%';
}
$get = filter_input_array(INPUT_GET, array(
            'model' => array(
                  'filter' => FILTER_CALLBACK,
                  'options' => 'check_empty_string'         
            ) ,
            'mark' => array(
                 'filter' => FILTER_CALLBACK,
                 'options' => 'check_empty_string'         
            ) ,
            'year' => array(
                 'filter' => FILTER_CALLBACK,
                 'options' => 'check_empty_string'         
            ) 
        ));

$query = sprintf('SELECT * 
FROM add_new_car , image_add_car 
WHERE id_add_car = user_id 
AND mark LIKE "%s"
AND model LIKE "%s"
AND year LIKE "%s"
ORDER BY id_add_car LIMIT 1',
$get['model'], $get['mark'], $get['year']);
//дальше работаем с запросом $query, хотя я бы использовал PDO!!!

function check_empty_string($string) {
            $string = trim($string);
            if (empty($string)) {
                return '%';
            }
            return $string . '%';
}
$get = filter_input_array(INPUT_GET, array(
            'model' => array(
                  'filter' => FILTER_CALLBACK,
                  'options' => 'check_empty_string'         
            ) ,
            'mark' => array(
                 'filter' => FILTER_CALLBACK,
                 'options' => 'check_empty_string'         
            ) ,
            'year' => array(
                 'filter' => FILTER_CALLBACK,
                 'options' => 'check_empty_string'         
            ) 
        ));

$connection = new PDO($connection_string);
$connection->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);

$query = 'SELECT add_new_car.*, 
GROUP_CONCAT(image_add_car.image_small) AS images_small
FROM add_new_car , image_add_car 
WHERE id_add_car = user_id 
AND mark LIKE :mark 
AND model LIKE :model 
AND year LIKE :year 
GROUP BY add_new_car.id
ORDER BY id_add_car';

//или как там называются поля в твоих таблицах "с картинками" ;)

$stmt = $connection->prepare($query);
$stmt->execute(array(
                ':mark' => $get['mark'],
                ':model' => $get['model'],
                ':year' => $get['year']
            ));

$messages = array();

while ($row = $stmt->fetchAll(PDO::FETCH_ASSOC)) {          
           $row['images_small'] = $row['images_small'] ? explode(',', $row['images_small']) : array();
           $messages[] = $row;
    }
/*
дальше работаем с массивом $messages!!!
трудно сказать какие у тебя там колонки ;) по этому массив будет выглядеть как-то так... ;)
$messages = array(
         'id' => 'blah-blah',
         'something' => 'blah-blah',
         'something1' => 'blah-blah',        
         'images_small' => array(
                  'images/small_1365172947.jpg',
                  'images/small_1365172948.jpg',
                  'images/small_1365172949.jpg'
         )
);
вывод на страницу будет примерно таким:
foreach($messages as $message) {
           echo($message['id']);
           echo($message['something']);          
           echo(isset($message['images_small'][0]) ? $message['images_small'][0] : 'not small image');
}
*/