How to display a field of type bLOB of mySQL in the page html

I have searched several times but I have not found a solution, I need to display an image that was saved as BLOB in the database.

Part of the code that saves to the database and displays the data

function manage_report($param1 = '', $param2 = '', $param3 = '')
{
    if ($this->session->userdata('doctor_login') != 1)
        redirect(base_url() . 'index.php?login', 'refresh');

    if ($param1 == 'create') {

        $data['img_principal'] = $this->input->post('img_principal');

        $this->db->insert('report', $data);
        $this->session->set_flashdata('flash_message', get_phrase('report_created'));
        redirect(base_url() . 'index.php?doctor/manage_report', 'refresh');
    }
    if ($param1 == 'edit' && $param2 == 'do_update') {

        $data['img_principal'] = $this->input->post('img_principal');

        $this->db->where('report_id', $param3);
        $this->db->update('report', $data);
        $this->session->set_flashdata('flash_message', get_phrase('account_updated'));
        redirect(base_url() . 'index.php?doctor/manage_report', 'refresh');

    } else if ($param1 == 'edit') {
        $page_data['edit_profile'] = $this->db->get_where('report', array(
            'report_id' => $param2
        ))->result_array();
    } 

    $page_data['page_name']  = 'manage_report';
    $page_data['page_title'] = get_phrase('manage_report');
    $page_data['reports']    = $this->db->get('report')->result_array();
    $this->load->view('index', $page_data);
}

As I'm trying to show on the .html page

<img src="<?php echo $row['img_principal']; ?>"/>

database

CREATE TABLE 'report' ( 'report_id' int(11) NOT NULL, 'img_principal' blo NOT NULL ) ENGINE=MyISAM DEFAULT CHARSET=utf8 COLLATE=utf8_unicode_ci;