Gagal update gambar pada php

saya masih pemula sehingga tidak mengerti mengapa gambar yang saya update tidak tampil / not found. berikut saya lampirkan controller serta viewnya..

Controller:

function petugas_update(){

$id_petugas = $this->input->post('id_petugas');
$nama = $this->input->post('nama');
$username = $this->input->post('username');
$password = $this->input->post('password');

$config['upload_path'] = './assets/upload/';
$config['allowed_types'] = 'jpg|png|jpeg';
$config['max_size'] = '2048';
$config['max_width'] = '1400';
$config['max_height'] = '1400';
$config['file_name'] = 'gambar'.time();

$this->load->library('upload',$config);
$where = array('id_petugas' => $id_petugas);
$data = array(
		'nama' => $nama,
		'username' => $username,
		'gambar' => $image['file_name'],
		'password' => md5($password)
		);

		if ($this->upload->do_upload('foto')){
		  $image = $this->upload->data();
		  unlink('assets/upload/'.$this->input->post('old_pict',TRUE));
		  $data['gambar'] = $image['file_name'];

		  $this->m_data->update_data($where,$data,'petugas');

		} else{
		  $this->m_data->update_data($where,$data,'petugas');
		}

$this->m_data->update_data($where,$data,'petugas');
redirect(base_url().'admin/petugas');

}

View:

<div class="container">
  <div class="card">
    <div class="card-header text-center">
      <h4><i class="fa fa-street-view"></i> Edit Librarian Details</h4>
    </div>
    <div class="card-body">
      <a href="<?php echo base_url().'admin/petugas' ?>" class='btn btn-sm btn-light btn-outline-dark pull-right'><i class="fa fa-arrow-left"></i> Back</a>
      <br/>
      <br/>

      <?php foreach($petugas as $p){ ?>
        <form method="post" action="<?php echo base_url().'admin/petugas_update'; ?>">
          <div class="form-group">
            <label class="font-weight-bold" for="nama">Full Name</label>
            <input type="hidden" value="<?php echo $p->id_petugas; ?>" name="id_petugas">
            <input type="text" class="form-control" name="nama" placeholder="Masukkan nama lengkap" required="required" value="<?php echo $p->nama; ?>">
          </div>
          <div class="form-group">
            <label class="font-weight-bold" for="username">Username</label>
            <input type="text" class="form-control" name="username" placeholder="Masukkan username" required="required" value="<?php echo $p->username; ?>">
          </div>

            <div class="form-group">
                <label class="font-weight-bold">Gambar</label><br />
                <?php
                if(isset($p->gambar)){
                  echo '<input type="hidden" name="old_pict" value="'.$p->gambar.'">';
                  echo '<img src="'.base_url().'assets/upload/'.$p->gambar.'" width="20%">';
                  }
                  ?>
                  <input name="foto" type="file" class="form-control">
           </div>

          <div class="form-group">
            <label class="font-weight-bold" for="password">New Password</label>
            <input type="password" class="form-control" name="password" placeholder="Type New Password">
          </div>

          <input type="submit" class="btn btn-primary" value="Save">
        </form>
      <?php } ?>

    </div>
  </div>
</div>