I didn't convert the ISO to img, I just formatted a USB drive for FAT and used dd:
sudo diskutil unmountdisk /dev/disk1
sudo dd if=./debian.iso of=/dev/disk1 bs=1m
I tested this with Debian 9.
It's important to note that the appropriate /dev/disk# should be determined by using the following command on the macOS command line:
diskutil list
In the question above, the USB device mapped to /dev/disk2 whereas the example above uses /dev/disk1. But the number could be 3 or 4 or some other number. Ensure the number correlates with the memory stick you use; you risk losing data if you get it wrong.
