Yes. Although modern BIOSs can boot from USB devices, they can not boot from an iso. You need to burn the .iso to disc, preferably RW so you can use it again I would suggest, and then transfer it over to the flash drive along with the bootimg files on the disc. Do a search for booting from USB flash for more details, as it also depends upon whether or not your particular machine needs to boot certain specialized files first if it does not inherently boot from USB.
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