How do I determine if an ISO is a hybrid?

Run the file command on the ISO image in question. The output from running this command on a non-hybrid ISO will look something like this

image.iso: ISO 9660 CD-ROM filesystem data 'foo' (bootable)

while the output from running this command on a hybrid ISO will look something like this

image.iso: DOS/MBR boot sector ISO 9660 CD-ROM filesystem data (DOS/MBR boot sector) 'foo' (bootable); partition 1 : ID=0x17, active, start-CHS (0x0,0,1), end-CHS (0x288,63,32), startsector 0, 1329152 sectors

Run fdisk on the file. If it shows anything meaningful, it is hybrid.

You can use this script to check the ISO image (-i flag for "inspect")

https://github.com/jsamr/bootiso

bootiso -i "your iso image"

Create a USB bootable device from an ISO image easily and securely.

Don't want to messup the system with dd command? Create a bootable USB from an ISO in one line [see it in action].

Works seamlessly with hybrid and non-hybrid ISOs (SYSLINUX or UEFI compliant) such as any linux ISO, Windows ISO or rescue live-cds like UltimateBootCD. You don't have to tweak anything: bootiso inspects the ISO file and chooses the best method to make your USB bootable.

You can run head -c 512 thefile.iso > bytes.txt.

In a proper non-hybrid ISO the bytes should all be zeros (maybe not visible by default in your text editor). Though in theory they could contain any random garbage, so in a non-zero case it is harder to confirm if it is a hybrid without more in-depth analysis of the bytes.

For Windows users you can install the gnuwin32 coreutils package to get that command.

This detects a partition table, not present at non-hybrid ROM media:

cat romdisk.iso 2>/dev/null | head -c 512 | tail -c 2 | xxd -p | grep -ie '55aa$'

What I don't know how to determine is between hybrid-ISO and harddisk image:

cat disk.img 2>/dev/null | head -c 512 | hexdump -vC