Upload single file (image) jquery

I'm making the upload of a single image in ajax. The problem is that the variable that should be saved the file is always undefined.

Here is the html code:

<form enctype="multipart/form-data" name='file'>
            <input type="file" name="file" id="foto-hidden" multiple style="float:left"/>

            <div class="pubblica"> Pubblica </div>
</form>

Here's the Ajax code:

$(document).on("click",'.pubblica', function()
{    
    var image = new FormData('file');

    jQuery.each($('#foto-hidden')[0].files, function(i, file) 
    {
        image.append('file-' + i, file);
    });

    if($("#option-select").val() != undefined)
    {
        id_squadra = $("#option-select").val();
    }

    $.ajax(
    {
        type: "POST",
        url: "",
        processData: false,
        contentType: false,
        data: { file: image, id_user: localStorage.getItem('id_user'), mobile: 1 }
    });

    //window.location = "index.html";
});

Who could help me? I do not understand why it behaves this way.