man geteltorito:

SYNOPSIS
       geteltorito <image|device> [-o outputfile]

DESCRIPTION
       geteltorito  is  a  Perl  script which extracts the initial/default El
Torito boot image from a CD if one exists. It will not extract any of other
boot images that are allowed by the El
       Torito standard.

       The boot image file is written to stdout and all other information
(e.g., image type and size) is written to stderr.  To write the image to a file
instead of stdout, specify the  output
       filename using -o filename.


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Testing:

$ geteltorito /mnt/d/install/linux_distrs/debian-6.0.0-i386-netinst.iso -o
eltorito
Booting catalog starts at sector: 1252
Manufacturer of CD:
Image architecture: x86
Boot media type is: no emulation
El Torito image starts at sector 7273 and has 4 sector(s) of 512 Bytes

....
Boot failed: press a key to retry...
Image has been written to stdout ....



How does it work:

$ geteltorito -o eltorito
/mnt/d/install/linux_distrs/debian-6.0.0-i386-netinst.iso
Booting catalog starts at sector: 1252
Manufacturer of CD:
Image architecture: x86
Boot media type is: no emulation
El Torito image starts at sector 7273 and has 4 sector(s) of 512 Bytes

Image has been written to file "eltorito".