With your ISO ready, and the USB you plan to flash ready, here's the steps to achieve victory.

  1. Your USB needs to be a bit bigger than the ISO, but the margin may vary.
    Remember that your USB will be erased during this process.

  2. Open a Terminal Window

  3. Run diskutil list and find your USB (/dev/diskN)

  4. Run diskutil unmountDisk /dev/diskN.
    It should print Unmount of all volumes on diskN was successful

  5. Run sudo dd if=<iso path> of=/dev/diskN bs=1m.
    Remember that both should be [absolute]. Your recommended block size may vary.
    This command also doesn't output anything mid-operation, but you can check on it's progress by CTRL+T

  6. Run diskutil eject /dev/diskN

If you need to, to convert an .iso to .img, run

hdiutil convert -format UDRW -o <img path> <iso path>