PHP和AJAX上传

So, I am a little new to using AJAX, I just have a question or two.

When I select an image, everything goes according to plans, if I choose to remove that photo, rather then uploading it the size of the image comes back as 9, why is that?

Will it always be 9?

Am I safe to do a if(filesize == 9) { //stuff }to tell if the user has removed the image before uploading?

Here is the javascript:

$("#chosenfile").change(function(){
     var data;

    data = new FormData();
    data.append( 'file', new Blob([$( '#chosenfile' )[0].files[0]], {type:"image/jpg"}) );

     $.ajax({
            url: '/includes/uploadimage.php',
            data: data,
            processData: false,
            contentType: false,
            type: 'POST',
            success: function ( data ) {
                alert( data );
                var json = JSON.parse(data);
                console.log(json);
            }
        });
});

Here is uploadimage.php:

<?php

    $Return = array();
    $Return["status"] = "success";
    $Return["image"] = "";

    $file = $_FILES["file"];
    $tmpName = $file["tmp_name"];

    echo json_encode($Return);

?>

I am getting this in my console:

{"status":"success","image":{"name":"blob","type":"image\/jpg","tmp_name":"\/tmp\/phpHWiMwv","error":0,"size":9}}