<?php
$startrow = $_GET['startrow'];

if (!isset($_GET['startrow']) or !is_numeric($_GET['startrow'])) {
  $startrow = 0;
} else {
  $startrow = (int)$_GET['startrow'];
}
?>
<?php

$db = mysqli_connect("localhost", "root", "", "media");
$uploaded = mysqli_query($db, "SELECT * FROM images LIMIT $startrow, 30");

while ($row = mysqli_fetch_array($uploaded)) {
    echo "<div class='img_container'>";
    echo "<li><img class='img_box' src='uploads/images/".$row['image_title']."' ></li>";
    echo "</div>";
}

$prev = $startrow - 30;
if ($prev >= 0) {
    echo '<div class="prevRow"><a href="'.$_SERVER['PHP_SELF'].'?page='.$page.'&startrow='.$prev.'">Back</a></div>';
}
    echo '<div class="nextRow"><a href="'.$_SERVER['PHP_SELF'].'?page='.$page.'&startrow='.($startrow+30).'">Next</a></div>';
?>