Here’s a simple way to create a bootable USB stick from a downloaded .ISO file on OS X.
Convert ISO to IMG
Open the terminal and type the following command:
hdiutil convert -format UDRW -o target.img source.iso
Remember to replace the paths in the previous example.
Transfer to USB stick
Warning: This will erase all data on your USB stick.
First, find the correct device node:
After you have successfully identified your USB stick, unmount the disk (replace N with the disk number):
diskutil unmountDisk /dev/diskN
Finally, transfer the image to the USB stick (again, replace N with the disk number):
sudo dd if=target.img of=/dev/rdiskN bs=1m
After a short while, depending on the image size, your USB stick will be ready to use as a bootable media.