Calling Up Thumbnail with Category Name

Would anyone know how to call up the most recently added photo added to a subcategory in a gallery-- to be placed with the subcategory name?  Someone mentioned that you could simply call up the photo with the highest ID at the time.  I'm new to PHP and I'm not sure how to go about doing this.  Need Help Please!  Here's some of my gallery code:  Is this the page it should go on?

<?php

        // initialization
        $result_array = array();
        $counter = 0;

        $cid = (int)($_GET['cid']);
        $pid = (int)($_GET['pid']);

        // Category Listing

 if(!$cid)
 {
echo "Select a category";
} else if ($cid && !$_GET['thumb']) {
            
 $result = mysql_query( "SELECT * FROM gallery_category WHERE parent_id = $cid" );
$num = 1;
echo "<table width='100%' border=1><tr>";
                        
while( $row = mysql_fetch_array( $result ) )
                {
$catname = $row['category_name'];
$catid = $row['category_id'];
                        
 echo "<td><a href='album.php?cid=".$catid."&thumb=1&ocid=$cid'>".$catname."</a></td> ";
 if ($num == '3') {
 echo "</tr><tr>";
 $num = 0;
 }
 $num ++;
                              
  }
echo "</tr></table>";
 }

// Thumbnail Listing

else if( $cid && $_GET['thumb'] )
 {
                $number_of_thumbs_in_row = 4;

                // If current page number, use it
                // if not, set one!

                if(!isset($_GET['page'])){
                    $page = 1;
                } else {
                    $page = $_GET['page'];
                }

                // Define the number of results per page
                $max_results = 12;

                // Figure out the limit for the query based
                // on the current page number.
                $from = (($page * $max_results) - $max_results);

                $result = @mysql_query( "SELECT photo_id,photo_caption,photo_filename FROM gallery_photos WHERE photo_category='".addslashes($cid)."' LIMIT $from, $max_results");

                $nr = @mysql_num_rows( $result );

                if( empty( $nr ) )
                {
 $result_final = "\t<tr><td><div align=\"center\"><strong>No images in category found!</strong>
<br><br><font size=\"2\"><a href='album.php?cid=".$_GET['ocid']."'>Back to Photo Gallery Category List</a></font>
 </div></td></tr>\n";
                }
                else
                {
                        while( $row = mysql_fetch_array( $result ) )
                        {
                                    
//this is where we were able to add a caption/etc. under our thumbnail in the gallery.
                        $result_array[] = "<a href='album.php?cid=$cid&pid=".$row[0]."'><img src='".$images_dir."/tb_".$row[2]."' border='0' alt='".$row[1]."' /><br />".$row[0]."</a>";
                        }
                                    
                        mysql_free_result( $result );
                                    
                        $result = @mysql_query( "SELECT category_name FROM gallery_category WHERE category_id='".addslashes($cid)."'" );
                        list($category_name) = mysql_fetch_array( $result );
                        mysql_free_result( $result );
                                    
$result2 = @mysql_query( "SELECT category_name FROM gallery_category WHERE category_id='".addslashes($_GET['ocid'])."'" );
$row = mysql_fetch_object( $result2 );
$ocid = $row->category_name;
$result_final = "<tr><a href='album.php?cid=".$_GET['ocid']."'>$ocid</a> &gt; $category_name<br><br>";
                                    
//Think this might also be where you can add your caption below image?
                                     
                                             
 foreach($result_array as $thumbnail_link)
                        {
                                if($counter == $number_of_thumbs_in_row)
                                {        
                                        $counter = 1;
                                        $result_final .= $category_link."\n</tr>\n<tr>\n";
                                }
                                else
                                $counter++;

                                $result_final .= "\t<td><div align=\"center\">".$thumbnail_link."</div></td>\n";
                        }
       
                        if($counter)
                        {
                                if($number_of_photos_in_row)
                        $result_final .= "\t<td colspan='".($number_of_thumbs_in_row)."'></td>\n";
                        $result_final .= "</tr>\n";
                                    
                                    
// Figure out the total number of results in DB:
$total_results = mysql_result(mysql_query("SELECT COUNT(*) as Num FROM gallery_photos WHERE photo_category=".addslashes($cid).""),0);
$select_list = "<select size=\"1\" onchange=\"document.location=this[this.selectedIndex].value\">";

// Figure out the total number of pages. Always round up using ceil()
$total_pages = ceil($total_results / $max_results);

//Below here is where I have my prev/next page links.