This works for almost all ISO's Ifind (at least Linux based):
sudo dd if=CentOS-6.9-x86_64-minimal.iso of=/dev/sdg bs=20M
20+1 records in
20+1 records out
427819008 bytes (428 MB) copied, 118.233 s, 3.6 MB/s
Of course change the .iso filename above and the /dev/sdg to your desired USB drive!........
This is useful if you are installing Windows and need virtio but of course Windows needs the virtio driver which is on a second iso.
This is the line of code you would add to your kvm startup script and then you get this iso as second cdrom you can browse to for your Windows install of virtio driver's or whatever other use you need it for.