btnsubmit.click(function(){
            var file_data = $('#uploaded_img').prop('files')[0];
            var form_data = new FormData();
            form_data.append('file', file_data);

            $.ajax({
                url: 'upload_img_custom.php',
                cache: false,
                contentType: false,
                processData: false,
                data: form_data,
                type: 'POST',
                success: function(php_script_response){
                    alert(php_script_response);
                }
            });
        });

<?php
    $upload_directory = "../uploads/Customized/";
    if (isset($_FILES['uploaded_img']))
    {
        $uploadedFileName=$_FILES['uploaded_img']['name'];
        $targetPath=time().$uploadedFileName; //time is concatenated to make filenames unique
        if($uploadedFileName != '')
        {
            $targetPath=time().$uploadedFileName;
            move_uploaded_file($uploadedFileName, $upload_directory."".$targetPath);
        }
    }
    header('Location: customize.php?upload=success');
?>

<form method=POST id=customize-form action ="" enctype=multipart/form-data>
     <div id=step3 class='options step'>
        <section class=section-title>Image</section>
        <div class=image-display><img id=image-disp src="" width=99 style="text-align:center" /></div> //div for displaying uploaded image
        <section style="margin-bottom:10px">
            <label class="paragraph-font2 full-width">Choose what you want on the top of your cake:</label>
        </section>
        <section style="margin-bottom:15px">
            <input class="paragraph-font2 full-width" type=file name=uploaded_img id=uploaded_img accept="image/*">
        </section>
    </div>
    <button type=submit class='btn btn-info action submit'><span class='glyphicon glyphicon-shopping-cart'></span> Add to cart</button>
</form>