Here is a handy list of commands using macosx native diskutil command. In my case for creating a USB image of Moblin v 2.0 for my atom powered Acer Aspire One Z5.

$ diskutil list
$ diskutil unmountDisk /dev/diskN
$ sudo dd if=/path/to/downloaded.img of=/dev/diskN bs=1024
$ sudo dd if=moblin-2.0-final-20090924-001.img of=/dev/disk4
Password:
1476608+0 records in
1476608+0 records out
756023296 bytes transferred in 1924.583704 secs (392824 bytes/sec)
$ diskutil eject /dev/diskN

Of course you must be quite sure about the device that is mounted. It’s better to issue the “diskutil list” command before pluging the USB device that you want to convert into image.

via nerdlogger