For OS X Maverick

Get a list of drives on your computer

diskutil list

Unmount the appropriate drive

diskutil unmountDisk /dev/install the ISO Image on>

Copy file to the drive you want to mount the isoimage on

dd if=<path of ISO Image> of=<path of your USB Drive>

For macOS Sierra

sudo /Applications/Install\ macOS\ Sierra.app/Contents/Resources/createinstallmedia --volume /Volumes/Untitled --applicationpath /Applications/Install\ macOS\ Sierra.app

Thank You