Display random image from database using PHP

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SQL

PHP

database

image

i want to display image with randomly selected or the one that i choose from database.
but i don't really know how to code it properly.

What I have tried:

$query1=mysqli_query($db_con,"select * from image_tb");
   while($row=mysqli_fetch_array($query1)){
   $img = "";
   $image_number = $row['id'];
   
   

<div class="block-content collapse in">
     <div class="row-fluid padd-bottom">
     <div class="span3">
//i want to display here the first image on my database but i don't how to code it properly. 
      <a href="#" class="thumbnail">
      if (1 == $image_number){
          <?php echo "$img"; ?>
      }
       </a>
       </div>
       <div class="span3">
//the 2nd image from database
      <a href="#" class="thumbnail">
      if (2 == $image_number){
          <?php echo "$img"; ?>
      }
      </a></div><a href="#" class="thumbnail">
       </a><div class="span3"><a href="#" class="thumbnail">
//3nd image 
      </a><a href="#" class="thumbnail">
      if (1 == $image_number){
          <?php echo "$img"; ?>
      }
       </a>
       </div>
<div class="span3">
//4th image 
      <a href="#" class="thumbnail">
      if (1 == $image_number){
          <?php echo "$img"; ?>
      }
       </a>
       </div>
     </div>
<?php
  }
?>
     </div>