<?php
//get URL of image from form input
$img = $_POST[ 'image' ];
//add image to media library and get its ID
$img = pods_attachment_import( $img );
//create array of data to be added
//You can add additional fields here if you want
$data = array(
'image_field' => $img ,
);
//get pods object for item of ID $id
$pod = pods( 'pod_name', $id );
//update the item and return item id in $item
$item = $pod->save( $data);