django - uploading file using ajax fails

I am trying to upload picture using ajax in django. When I post the usual way without ajax, it gets uploaded as expected. But when I upload using ajax, I get the success function, but my form gets invalid in the view and the data I get is from the else condition in the view:

{"image":["This field is required."]}

js:

$('#settings-dialog #background-settings #image-device #upload').on('click', function() {
    var modify_frm = $('#settings-dialog #background-settings #image-device #upload-form');
    $.ajax({
        type: modify_frm.attr('method'),
        url: modify_frm.attr('action'),
        data: modify_frm.serialize(),
        dataType: 'json',
        success: function(data) {
            $('#settings-dialog #background-settings #image-device #upload').text(data);
        },
        error: function(data) {
            $('#settings-dialog #background-settings #image-device #upload').text(JSON.stringify(data));
        }
    });
});

What am I missing here? Could you please help me solve this.

View with ajax don't work:

@login_required(login_url='/custom123user/login')
def admin_page_snap_add(request, page_id):
    if not request.user.is_admin:
        return render(request, 'admin_login_invalid.html')
    else:
        page = Page.objects.get(id=page_id)
        if request.user == page.user:
            if request.is_ajax() and request.POST:
                form = PageSnapForm(request.POST, request.FILES)
                if form.is_valid():
                    page_snap = form.save(commit=False)
                    page_snap.page = page
                    page_snap.user = page.user
                    page_snap.save()
                    data = 'Uploaded'
                    return HttpResponse(json.dumps(data), content_type='application/json')
                else:
                    data = form.errors
                    return HttpResponse(json.dumps(data), content_type='application/json')
            else:
                raise Http404
        else:
            return render(request, 'wrong_user.html')