How Do I Retrieve Images Dynamically Based On The Login Username?

I have created a site in Joomla with a login (no self registration,
users are provided with username and password by the admin).
The users are supposed to login to a specific page where they can see
4 images.
I have the following code:
<?php
// define directory path
$dir = "images/user1/";

// iterate through files
// look for JPEGs
if (is_dir($dir)) {
if ($dh = opendir($dir)) {
while (($file = readdir($dh)) !== false) {
if (preg_match("/.jpg/", $file)) {
// read EXIF headers
$exif = exif_read_data($file, 0, true);
echo "<tr>";
// get thumbnail
// link to full image
echo "<td valign=top><a
href=$dir/$file><imgsrc=thumbnail.php?file=$file></a><td>";
echo "<td valign=top><font size=-1>";
// get file name
echo "File: <b>" . $exif['FILE']['FileName'] .
"</b><br/>";
// get timestamp
echo "Timestamp: " . $exif['IFD0']['DateTime'] .
"<br/>";
// get image dimensions
echo "Dimensions: " . $exif['COMPUTED']['Height'] . "
x " . $exif['COMPUTED']['Height'] . " <br/>";
// get camera make and model
echo "Camera: " . $exif['IFD0']['Model'];
echo "</font></td>";
echo "</tr>";
}
}
closedir($dh);
}
}
?>

The question now is how to change the code to dimamically replace the
folder name by the login username used.
For example....if user2 logs in the images loaded will be only those
in the folder images/user2, if user3 logs in it will be from the
folder images/user3, etc...
I am a little confused as to how to implement that in Joomla but as
long as I have the code right I thinkI can just insert the code into
the appropriate page using a mambot.
If anybody here has any tips on how to accomplish that it would be
extremely appreciated.

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