image resizing does not work for Upload module

I have installed Drupal 4.7.0 and also finished following settings

File system settings:
File system path = files , download method = private , Temporary directory:C\Junk

Upload Settings:
Maximum resolution for uploaded images:640x480. (For image resizing).

Q. When I upload any file which has resolution more than 640x480, upload module does not generate massage that file has been resized and not even resized it.

What could I interpret is that in _upload_image($file) function (upload. module)
$result=image_scale($file->filepath, $file->filepath, $width, $height);
is not working and return false every time.

I am facing problem for image resizing and I want work out with Drupal default behavior only so that I can avoid others image related module.
So please reply?