Array
(
    [0] => Array
        (
            [id] => 2
            [first_name] => sandeep
            [last_name] => sharma
        )

    [1] => Array
        (
            [id] => 3
            [first_name] => Gaurav
            [last_name] => Jain
       )

Array
(
    [0] => Array
        (
            [id] => 2
            [first_name] => sandeep
            [last_name] => sharma
            [image] =array
                (
                    [0] => Array
                        (
                            [image] => abc.jpg
                        )
                    [1] => Array
                        (
                            [image] => abcdef.jpg
                        )
                )
        )

    [1] => Array
        (
            [id] => 3
            [first_name] => Gaurav
            [last_name] => Jain
            [image] =array
                (
                    [0] => Array
                        (
                            [image] => abcdefghi.jpg
                        )
                )
       )

$rows = $query->result_array(); //current array
            array_push($rows, array("image"=>$image));  //$image is second array(where image save as array)