Database

.......
                sql = "select " + picField + " from " + table + " where " + where;
                conn = new SqlConnection(connectionstring);
                byte[] picture = (byte[])ExecuteScalar(sql);  // Shows error
                Image source = Image.FromStream(new MemoryStream(picture));
                Image th = source.GetThumbnailImage(w, h, null, IntPtr.Zero);
.......
        public object ExecuteScalar(string strCommand)
    {
        object res=null;
        conn.Open();
        SqlCommand cmd = new SqlCommand(strCommand, conn);
        try
        {
            res = cmd.ExecuteScalar();
        }
        catch(Exception e)
        { res = e.Message; }
        finally
        {
            conn.Close();
        }
        return res;
    }