<?php
 
$str = 'Hi my name is Harry you can find my website here: http://w...content-available-to-author-only...x.com. Oh and what do you think of my my wife: http://w...content-available-to-author-only...e.com/wife.jpg?';
$r1 = '/(http:\/\/[\S]+(?:jpg|jpeg|png|gif))/';
$r2 = '/(?<!src=")(http:\/\/[\S]+\b)/';
$sub1 = '<img src="$1"/>';
$sub2 = '<a href="$1">$1</a>';
$res = preg_replace($r1, $sub1, $str);
$result = preg_replace($r2, $sub2, $res);
echo $result;

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