Description
void 
passthru ( string command [, int &return_var] )
   The passthru() function is similar to the
   exec() function in that it executes a
   command. This function
   should be used in place of exec() or
   system() when the output from the Unix command
   is binary data which needs to be passed directly back to the
   browser.  A common use for this is to execute something like the
   pbmplus utilities that can output an image stream directly.  By
   setting the Content-type to image/gif and
   then calling a pbmplus program to output a gif, you can create
   PHP scripts that output images directly.