How to transfer images trough POST method in PHP - php

Question

I want to send an already existing image stored in the $_FILES['the_file']. The $_FILES['the_file'] is from the page "img_upload.php" for uploading that image, then it is sent to the "form.php" page where the rest of the form is, and then sent to the processing page named "add_product.php"
My problem is that I want to send the $_FILES['the_file'] from the form on "form.php" page to "add_product.php" page (with the rest of the form from "form.php"). How can I do that?
Here is my code:
// img_upload.php
<form action="form.php" method="post" enctype="multipart/form-data">
<input type='file' name='the_file' class='image-selector'>
<button type="submit">Insert the picture</button>
</form>
// form.php
<?php
$file = $_FILES['the_file'];
$fileName = $_FILES['the_file']['name'];
$fileSize = $_FILES['the_file']['size'];
$fileTmpName = $_FILES['the_file']['tmp_name'];
$fileType = $_FILES['the_file']['type'];
?>
<p>Picture name: <?php echo $fileName; ?></p>
<form action="../Includes/add_product.php" method="post" enctype="multipart/form-data">
<?php
echo "<input type='hidden' name='file' value=".$file.">";
?>
<input type="text" name="price" placeholder="Name the price">
<input type="text" name="sent_from" placeholder="Sent from">
<input type="text" name="category" placeholder="Select the category">
<button type="submit">Insert the product</button>
</form>

Answer 1

If you want to include it in a hidden input then you'll need to encode it as a string. The usual way to do that is to base64 encode it.
This question covers how to do that.
When you insert the string into the document, do make sure you make use of htmlspecialchars so you don't expose yourself to XSS attacks.
That approach involves sending the file to the server, then sending it (in a less compressed form) back to the browser, then sending it back to the server again.
This is not bandwidth efficient!
Usually the approach for this would be the same the file on the server and then send an id (e.g. the file name) back to the client (and have some logic for cleaning up old files left over from the user abandoning the process part way through).