image dimension in php code args

I used this code, but nothing happen, maybe there is something small detail missing thankyou who ever may help

$mimes = array( 'image/jpeg');
                if( !in_array( $file['type'], $mimes ) )
                    return $file;
                $image = getimagesize($file['tmp_name']);

                $minimum = array(
                    'width' => '400',
                    'height' => '400'
                ); 
                $maximum = array( 
                    'width' => '400',
                    'height' => '400'
                );
                $image_width = $image[0];
                $image_height = $image[1];

                if ( $image_width < $minimum['width'] || $image_height < $minimum['height'] ) {
                    $adOK = 0; $post_new_error['job_img']       = __('Image dimension too small');                      
                }
                elseif ( $image_width > $maximum['width'] || $image_height > $maximum['height'] ) {
                    $adOK = 0; $post_new_error['job_img']       = __('Image dimension too big');        
                }