1. Download the .iso file. This also can be an .img file or a .dmg file

2. Rename the .iso file to .dmg.

3. Right-click on the .dmg file and select Get Info. Write down the full path name as mentioned in the dialog box. We will need that for step 9.

4. Start a Terminal window. The Terminal application is located in the folder /Applications/Utilities/ of your Macintosh HD volume.

5. In the Terminal window, type: diskutil list and press the Enter key. Now a list of your storage devices is displayed in the Terminal window, underneath what you typed earlier.

6. Put the USB stick in the USB port of your Mac.

7. In the Terminal window, type again:

diskutil list

and press the Enter key. Now you see the same list, but with an extra storage device. The location of that device has the format /dev/diskN, where N is a number. In my case it was /dev/disk1. Write that down.

8. In Terminal, type

diskutil unmountDisk /dev/diskN

and press the Enter key. Use the N from step 7. This will unmount the USB stick (it will disappear from your desktop).

9. In Terminal, type

sudo dd if=/path/to/file.dmg of=/dev/diskN bs=1m

and press the Enter key, where /path/to/file.dmg is the full path from step 3, and /dev/diskN from step 7. You will be asked to enter a password. This is why you must be logged in as an administrator, a non-administrator does not have to privileges to perform this operation. This operation takes quite a while (seconds in my case). Be patient and let it do its thing.

10. In Terminal, type

diskutil eject /dev/diskN

and press the Enter key. Again N is the number we established in step 7.

11. You are done.