Cant get data from C#, returned one row table data in json?

[WebMethod]
public static GalleryDetailsInPopup[] BindDatatable(int imageId)
{
DataTable dt = new DataTable();
List<GalleryDetailsInPopup> details = new List<GalleryDetailsInPopup>();
using (SqlConnection con = new SqlConnection("Server=SERVER1; Database=WomensClothing; uid=sa; pwd=elife@123"))
{
using (SqlCommand cmd = new SqlCommand())
{
cmd.CommandText = "Get_galleryImages";
cmd.CommandType = CommandType.StoredProcedure;
cmd.Parameters.AddWithValue("@imageId", imageId);
cmd.Connection = con;
con.Open();
SqlDataAdapter da = new SqlDataAdapter(cmd);
da.Fill(dt);
foreach (DataRow dtrow in dt.Rows)
{
GalleryDetailsInPopup popupDetails = new GalleryDetailsInPopup();
popupDetails.ImageId = Convert.ToInt32(dtrow["ImageId"].ToString());
popupDetails.OwnerName = dtrow["OwnerName"].ToString();
popupDetails.FrontImage = dtrow["FrontImage"].ToString();
popupDetails.BackImage = dtrow["BackImage"].ToString();
popupDetails.DesignedBy = dtrow["DesignedBy"].ToString();
popupDetails.FrontStyle = dtrow["FrontStyle"].ToString();
popupDetails.BackStyle = dtrow["BackStyle"].ToString();
popupDetails.BodyFabric = dtrow["BodyFabric"].ToString();
popupDetails.SleeveFabric = dtrow["SleeveFabric"].ToString();
popupDetails.YokeFabric = dtrow["YokeFabric"].ToString();
popupDetails.CollerFabric = dtrow["CollerFabric"].ToString();
popupDetails.Price = Convert.ToDouble(dtrow["Price"].ToString());
details.Add(popupDetails);
}
}
}
return details.ToArray();
}

$(document).on("click", "[id*=link" + data.d[i].ImageId + "]", function () {
                        var imageId = $(this).closest("td").find('span').html();
                        alert(imageId);
                        $.ajax({
                            type: "POST",
                            contentType: "application/json; charset=utf-8",
                            url: "gallries.aspx/BindDatatable",
                            data: "{'imageId':'" + imageId + "'}",
                            dataType: "json",
                            success: function (popup) {
                                var frontstyles = popup.ImageId;
                                alert(frontstyles);

                            },
                            error: function (result) {
                                alert("Error");
                            }
                        });

                    });