Below is the code for file upload in CodeIgniter:

To Configure file upload, limit by size, types, and upload path.

//Upload Photo
$config['upload_path'] = './uploads/';
$config['allowed_types'] = 'gif|jpg|png';
$config['max_size']    = '5000';
//Rename the uploaded image
$config['file_name'] = <NEW IMAGE NAME>;

With this, you can call upload library

$this->load->library('upload', $config);

change the photo to any variable given in the HTML Form.

if ( ! $this->upload->do_upload('photo')){
      $result['error'] = $this->upload->display_errors('','');
 }else{
      $image = $this->upload->data();
 }

If you want to resize Image

    $config['image_library'] = 'gd2';
    $config['source_image'] = $imagepath;
    $config['create_thumb'] = TRUE;
    $config['maintain_ratio'] = TRUE;
    $config['width'] = 320;
    $config['height'] = 480;

With this, you can call image library

        $this->load->library('image_lib', $config);

and let the image library work for you:

if ( ! $this->image_lib->resize())
 {
       echo$this->image_lib->display_errors('','')
 }else{
       $img = $this->image_lib;
       echo $img->full_dst_path;
 }