Problem does not save the image in the database

I have the problem that when I want to upload a photo to show it, it is not saved in the database and instead of being saved it takes the value of "empty"

the methods I use are these

class comentarios{

    static function agregar($comentario, $CodUsua, $CodPost,$imagen2)
    {
        $con = conexion("root", "");
        $consulta = $con->prepare("insert into comentarios(comentario, CodUsua, CodPost,Imagen) values(:comentario, :CodUsua, :CodPost,:Imagen) ");
        $consulta->execute(array(
                    ':comentario' => $comentario,
                    ':CodUsua' => $CodUsua,
                    ':CodPost' => $CodPost,
                    ':Imagen' => $imagen2
                    ));
    }


    static function mostrar($CodPost)
    {
        $con = conexion("root", "");
        $consulta = $con->prepare("select U.nombre, C.comentario,C.imagen from usuario U inner join comentarios C on U.CodUsua = C.CodUsua where C.CodPost = :CodPost");
        $consulta->execute(array(':CodPost' => $CodPost));
        $resultado = $consulta->fetchAll();
        return $resultado;
    }
}