osx - disk utility, restore to usb drive but get "resource is busy"

I was trying to create a bootable usb drive instead of a dvd but kept getting resource is busy when clicking  "scan image" required by the disk utility.

Turns out you have to mount the source image .dmg file (.iso are selectable as source images) , click on the mounted volume in disk utility, and choose restore on that one and select the proper source/destinations. Destination needs to be a formatted partition on the external that's mounted.