<?php
require_once __DIR__ . '/connection.php';

$id = isset($_POST['id']) ? $_POST['id'] : '';
$img_id    = $_POST['img_id'];
$img_path  = $_POST['img_path'];
$type      = $_POST['type'];
$user_id   = $_POST['user_id'];
$sessionID = $_POST['sessionID'];


$data = array();      // array to pass back data

$check = $dbConnect->prepare('DELETE FROM drucker 
WHERE id      = :prod_id
AND img_id    = :img_id
AND img_path  = :img_path
AND type      = :type
AND user_id   = :user_id
AND sessionID = :sessionID');


$check->bindValue(':prod_id',          $id);
$check->bindValue(':img_id',       $img_id);
$check->bindValue(':img_id',       $img_id);
$check->bindValue(':img_path',   $img_path);
$check->bindValue(':type',           $type);
$check->bindValue(':user_id',     $user_id);
$check->bindValue(':sessionID', $sessionID);

if ($check->execute() === true) {
    $data['success'] = true;
} else {
    $data['success'] = false;
}

// return all our data to an AJAX call
echo json_encode($data);
?>

ce serait bien plus simple, pour supprimer, de passer un seul paramètre, l'id du produit.
quel est le contenu généré par cette boucle : while ($prod = $req->fetch(PDO::FETCH_ASSOC)) { ?>
les champs cachés ont-ils la valeur attendue ?

<?php
require_once __DIR__ . '/connection.php';

$id        = $_POST['id'];
$img_id    = $_POST['img_id'];
$type      = $_POST['type'];
$user_id   = $_POST['user_id'];
$sessionID = $_POST['sessionID'];
$location  = $_POST['location'];
$path      = $_POST['img_path'];
$time      = $_POST['time'];

$check = $dbConnect->prepare('SELECT COUNT(*) FROM drucker 
WHERE prod_id = :id
AND img_id    = :img_id
AND img_path  = :img_path
AND type      = :type
AND user_id   = :user_id
AND sessionID = :sessionID');

$check->bindValue(':id',               $id);
$check->bindValue(':img_id',       $img_id);
$check->bindValue(':img_path',       $path);
$check->bindValue(':type',           $type);
$check->bindValue(':user_id',     $user_id);
$check->bindValue(':sessionID', $sessionID);
$check->execute();

if ((int)$check->fetchColumn() === 0) {
    $stm = $dbConnect->prepare('INSERT INTO drucker (prod_id, img_id, img_path, type, user_id, sessionID, zeit) VALUES (:prod_id, :img_id, :img_path, :type, :user_id, :sessionID, :time)');
    $stm->bindValue(':prod_id',          $id);
    $stm->bindValue(':img_id',       $img_id);
    $stm->bindValue(':img_path',       $path);
    $stm->bindValue(':type',           $type);
    $stm->bindValue(':user_id',     $user_id);
    $stm->bindValue(':sessionID', $sessionID);
    $stm->bindValue(':time',           $time);
    $stm->execute();
}

header("Location:" . $location);?>

<?php
require_once __DIR__ . '/connection.php';

$img_id = $_POST['img_id'];
$img_path = $_POST['img_path'];
$type = $_POST['type'];
$user_id = $_POST['user_id'];
$sessionID = $_POST['sessionID'];


$data = array();      // array to pass back data

$check = $dbConnect->prepare('DELETE FROM drucker 
WHERE img_id  = :img_id
AND img_path  = :img_path
AND type      = :type
AND user_id   = :user_id
AND sessionID = :sessionID');

$check->bindValue(':img_id', $img_id);
$check->bindValue(':img_path', $img_path);
$check->bindValue(':type', $type);
$check->bindValue(':user_id', $user_id);
$check->bindValue(':sessionID', $sessionID);
//$check->execute();

if ($check->execute() === true) {
    $data['success'] = true;
} else {
    $data['success'] = false;
}

// return all our data to an AJAX call
echo json_encode($data);
?>

<?php 
$req = $dbConnect->query('SELECT * FROM drucker WHERE sessionID = "' . $session . '"');

$i = 1;
        while ($prod = $req->fetch(PDO::FETCH_ASSOC)) { ?>
            <tr>
                    <form class="remove" method="post" action="drucker_remove.php" name="<?php echo $prod['id'] ?>">
                        <input type="hidden" name="img_id" value="<?php echo $prod['img_id'] ?>">
                        <input type="hidden" name="type" value="<?php echo($prod['type']) ?>">
                        <input type="hidden" name="img_path" value="<?php echo($prod['img_path']) ?>">
                        <input type="hidden" name="user_id" value="<?php echo $_SESSION['user_id'] ?>">
                        <input type="hidden" name="sessionID" value="<?php echo $_SESSION['sessionID'] ?>">
                        <input type="submit" value="Löschen" name="remove_img">
                    </form>
            </tr>

        <?php } ?>