To back up your Raspberry Pi SD card follow these simple steps.
Command Line Approach
Step 1: Run diskutil list from the command line
Step 2: Determine the SD card of the Pi, and unmount it with diskutil unmount /dev/disk2s1
Step 3: Save the file to your hard drive with the following command: sudo dd bs=16m if=/dev/rdisk2 of=backup.img
and to restore: sudo dd bs=16m if=backup.img of=/dev/disk2
If you are impatient you can hit CTRL + T to get status of the transfer
GUI Approach
There are many ways to back back up your Pi's SD card, but I have found this one the easiest to remember how to do only doing it once or twice a year since it uses Disk Utility.
If you haven't given Disk Utility "Full Disk Access" You will need to do these steps only once.
Step 1: In your Preferences go to > Security and Privacy > Privacy
Step 2: Hit lock button and enter password
Step 3: Hit the + button, search disk utility and add, save and close out
Once that is done backing up is easy and can be done with only a few clicks.
Step 1: Open Disk Utility, hit ⌘2 so all disks are shown
Step 2: Right click on the top level volume of the SD card you want to back up and select Image From .... It's "Centon DS" in my example below
Step 3: Name the file what you want but before you save change the format from read-only to compressed or read/write depending on your needs.
That's it folks! 3 very quick steps to backing up your Raspberry Pi SD card on a Mac! With the ISO file you can easily use Etcher to deploy the image on other Pi's or replace a worn out SD card.
I hope you find this helpful!