hur kontrollerar jag om mysql-frågan inte returnerar något resultat (posten hittades inte) med php?

Du kan använda mysqli_num_rows() i mysqli

if(mysqli_num_rows($result) > 0){

    while($row = mysqli_fetch_array($result))
    {
        $totalRows++;

        echo "<tr>";
        echo "<td>" . $row['ID'] ."(".$totalRows. ")</td>";
        echo "<td>" . $row['name'] . "</td>";
        echo "<td>" . $row['imgPURL'] . "</td>";
        echo "<td>" . $row['imgUrl'] . "</td>";  
        echo "</tr>";         
    }
} else {
    echo "<tr><td colspan='4'>Not Found Image:".$line.'</td></tr>';
}