Put the SD card in your Mac.
Start a terminal window and type the following command:
Search for your SD card and write down the disk number. Let’s assume we need disk2.
sudo dd if=/dev/disk2 of=~/Desktop/BackupDisk2.img bs=1M
Wait until the SD card has been completely read. The command does not show any feedback, so wait for the command prompt to reappear in the terminal window once it is complete.
Before we can restore a image to a SD card, first we need to unmount it:
diskutil unmountDisk /dev/disk2
Now type the command to restore the image file to the SD card:
sudo dd bs=1m if=~/Desktop/BackupDisk2.img of=/dev/disk2 conv=sync
After restoring, eject the disk2:
sudo diskutil eject /dev/disk2