The Disk Utility program in Mac OS X enables you to create disk images (.dmg), similar to those you encounter when you install software on your Mac. When you double-click on this type of file, your computer mounts it as though it were a DVD or hard drive. In fact, you can think of mounted disk images as virtual drives. You can also add password protection to disk images when you create them. Without the correct password, it’s almost impossible to read the contents of an encrypted disk image, so it’s a great way to transfer data securely via flash drive, CD, or DVD or travel with files you want to keep confidential.
It's important to note, however, that the Macintosh Disk Utility does not replace the use of FileVault for storing data more permanently on a dekstop or laptop Mac. Remember, too, that Level 1 data must be permanently removed from portable devices if it is not covered by a current and approved business need.
To create a disk image from a folder on your Mac, first open Disk Utility. You’ll find it in the Utilities folder inside the Applications folder.
ITS has also prepared a short video tutorial to illustrate the process of creating a Disk Image.
Now you can transfer the disk image easily and securely via USB drive or other means. The only way to access the data inside the disk image is by entering the correct password.
Note that Disk Utility can make disk images from folders, but not from individual files. If you want to create a disk image for a single file, just create and name a new folder, place your file inside, and make a new disk image from that folder using the steps above.