Cant generate image for required email - php

Question

I want to write a program where I will insert a particular id through form in database and the corresponding email will be displayed in image in jpeg format.
But I am not getting the required email instead I am getting image with this text "No email upload".
I have 3 files in one folder
index.php,
connect_sql.php,
generate_image.php
Below is code in index.php
<?php
require 'connect_sql.php';
if(isset($_GET['id'])){
$id = $_GET['id'];
if(!empty($id)){
global $conn;
$escaped_id = mysqli_real_escape_string($conn,$id);
$query = "SELECT username,email FROM user_table WHERE id = ".$escaped_id;
$query_run = mysqli_query($conn,$query);
$num_rows = mysqli_num_rows($query_run);
if($num_rows == 1){
while($row = mysqli_fetch_assoc($query_run)){
$fetched_email = $row['email'];
$fetched_name = $row['username'];
echo $fetched_name." your email is ";
echo "<img src='generate_image.php' />";
}
}else{
echo "Id not found.";
}
}else{
echo "Please enter id.";
}
}
?>
<form action="index.php" method="get">
<p>
Id<br />
<input type="text" name="id" />
</p>
<p>
<input type="submit" value="Submit" />
</p>
</form>
Below is code in connect_sql.php
<?php
$hostname = "localhost";
$username = "root";
$password = "";
$db_name = "php_thenewboston";
$conn = mysqli_connect($hostname,$username,$password);
$conn_db = mysqli_select_db($conn,$db_name);
if(!$conn || !$conn_db){
die("Connection unsuccessful.");
}
?>
Below is code in generate_image.php
<?php
header('Content-type: image/jpeg');
if(!empty($fetched_email)){
$email = $fetched_email;
}else{
$email = "No email uploaded.";
}
$email_length = strlen($email);
$font_size = 16;
$imageHeight = ImageFontHeight($font_size);
$image_width = $imageHeight * $email_length;
$image = imagecreate($image_width,$imageHeight);
imagecolorallocate($image,255,255,255);
$font_color = imagecolorallocate($image,0,0,0);
imagestring($image, $font_size, 0, 0, $email, $font_color);
imagejpeg($image);
?>
I am unable to catch my error.
I am a beginner in php.
Please comment below for any query.