Adding radio button values to MYSQL table using PHP

i would like to know, what is the purpose of these two image TAG. i just changed those img tag into button image .

<h1>Assessment</h1>
<form action="save.php" method="post">
  <p class="p1"> Question 1</p>
  <p class="p4"> Are you tall or short?</p>
  <p class="p3">
    <input type="radio" name="q1" value="1" />
    1
    <input type="radio" name="q1" value="2" />
    2
    <input type="radio" name="q1" value="3" />
    3
    <input type="radio" name="q1" value="4" />
    4
    <input type="radio" name="q1" value="5" />
    5 </p>
  <br>
  <br>
  <input type="image" src="Images/image1.png" />
  <input type="image" src="Images/save.png" />
</form>

save.php

 <?php
    if (isset($_POST['q1'])){
        $q1 = $_POST['q1'];
        mysql_query("INSERT INTO assessment (q1) VALUES ('$q1')");
    }
    ?>

if (isset($_POST['q1'])) {
    $q1 = $_POST['q1'];
    $stmt = $db->prepare("INSERT INTO members (q1) VALUES (:q1)");

    $stmt->execute(array(':q1' => $_POST['q1']));
}