Command line
If you are comfortable with the command line, you can image a card without any additional software. Run:
diskutil list
Identify the disk (not partition) of your SD card e.g. disk4 (not disk4s1):
diskutil unmountDisk /dev/<disk# from diskutil> e.g. diskutil unmountDisk /dev/disk4 sudo dd bs=1m if=image.img of=/dev/<disk# from diskutil> e.g. sudo dd bs=1m if=2015-02-16-raspbian-wheezy.img of=/dev/disk4