How to force a file download

I’m working on a big script for Greg, a client of mine. He needed a way so the user can download an image without using the common method (right click on the image and then ‘Save image as’) but using a normal browser download box.
After few minutes of searching the www.php.net website I wrote this small function to help me doing this

 function ForceDownloadImage($path_to_image)
 {
  	//get filename
  	$filename = basename($path_to_image);
  	//sent the right headers
	header("Content-Transfer-Encoding: binary");
	header("Content-Type: image/jpg");
	header("Content-Disposition: attachment; filename=$filename");
	//start feeding with the file
	readfile($path_to_image);
 }

The “$path_to_image” variable can be an absolute path (“/dir1/dir2/file1.txt”), a relative path (“dir1/file1.txt”) or an URL (“http://www.domain.com/txt/abc.txt”).
The function will return a download box :

If you use this function then be very carefull as it can force download any type of file if used wrong!
So don’t “trust” your users and provide the script with a parameter in this form (force_download.php?path=/images/test.gif) but use a more secure way (for example : I have a DB table with all the images path and I give as a parameter only the imageID and based on it I retrieve the real path to the file )!!
I hope this will help someone