<?
$arr = array();
$arr[0]['image'] = 'pic.PNG';
$arr[1]['image'] = 'abouttown3.jpg';
$images = array();
if (! empty($arr)) {
  foreach ($arr as $row) {
    $images[] = $row['image'];
  }
}

echo "<br/> Existing";
echo '<pre>';
print_r($arr);
echo '</pre>';

echo "<br/> New";
echo '<pre>';
print_r($images);
echo '</pre>';

<br/> Existing<pre>Array
(
    [0] => Array
        (
            [image] => pic.PNG
        )

    [1] => Array
        (
            [image] => abouttown3.jpg
        )

)
</pre><br/> New<pre>Array
(
    [0] => pic.PNG
    [1] => abouttown3.jpg
)
</pre>