IMG and ISO files are complete images of physical media such as CD-ROMs, DVDs, floppy disks, etc. that contain all of the files and folders in a particular package.
To install any software package from an image, the image itself must first be "mounted" by the Operating System. This can be accomplished by:
Burning the image directly to DVD making sure to specify the source type as "image". Once the burning of the image is complete, the physical media can be inserted into the computer and will be recognized like any other DVD. You must have a writable DVD drive.
Burning the image directly to a USB thumbdrive. This is particularly useful for those people who have Netbooks or other computers without a writable DVD drive.
Note Burning the file to a disk as a "data disk" will simply end up with a .img or .iso file on the disk, which cannot be used for the installation.
Once you have successfully mounted your image, you can then launch the software install.
For a bootable installation, this means restarting your computer and booting from the bootable installation media you created.
For an executable installation, this means launching the installation application from the mounted image.
For detailed instructions on the steps required for burning and mounting an IMG or ISO file, refer to Working with Image Files. This document also includes specific instructions for burning the image directly to a USB thumbdrive.