[eluser]Sawariya[/eluser]
$config['image_library'] = 'GD';
$config['source_image'] = '/path/to/image/mypic.jpg';
$config['create_thumb'] = TRUE;
$config['maintain_ratio'] = TRUE;
$config['width'] = 75;
$config['height'] = 50;
$this->load->library('image_lib', $config);
$this->image_lib->resize();
dont copy this... change this code as per your requirement...
it will work properly