error in displaying image in Gridview

public class CAt : ICat
    {
        int _categoryid; string _categoryname; string _description; byte _image;
        public int categoryid
        {
            get
            {
                return _categoryid;
            }
            set
            {
                _categoryid = value;
            }
        }

        public string categoryname
        {
            get
            {
                return _categoryname;
            }
            set
            {
                _categoryname = value;
            }
        }

        public string description
        {
            get
            {
                return _description;
            }
            set
            {
                _description = value;
            }
        }

        public byte image
        {
            get
            {
                return _image;
            }
            set
            {
                _image = value;
            }
        }
    }
}

public List<cat> GetCategories()
        {
            List<cat> lst = new List<cat>();
            cn = new SqlConnection(con);
            string query = "Select Categoryid, categoryname, description, picture from Categories";
            cmd = new SqlCommand(query, cn);
            cn.Open();
            dr = cmd.ExecuteReader();
            try
            {
                while (dr.Read())
                {
                    CAt c = new CAt();
                    c.categoryid = (int)dr["categoryid"];
                    c.categoryname = dr["categoryname"].ToString();
                    c.description = dr["description"].ToString();
                    c.image = Convert.ToByte(dr["picture"]);
                    lst.Add(c);
                }
                return lst;
            }
            catch (Exception ex)
            {
                throw ex;
            }
            finally 
            {
                cn.Close();
            }
        }