To make a backup / clone of an SD card from within OS X, open Terminal and run
$ sudo dd if=/dev/disk2 bs=1m | gzip > ~/Desktop/raspberry_clone.gz (If you’re not sure what /dev/disk the SD card is, run
$ diskutil list and you’ll see where the SD Card is mounted).
It can take a while for the backup command to run, depending how big the SD Card is.
The command is also piping the ‘dd’ (copy a drive) to the ‘gzip’ command, which will compress the cloned image. This will leave you with a much smaller backup file.
To reload the backup gzip file to the SD card run the command:
$ gzip -dc ~/Desktop/raspberry_clone.gz | sudo dd of=/dev/disk2 bs=1m