A live install image contains a Debian system that can boot without modifying any files on the hard drive and also allows installation of Debian from the contents of the image.
Is a live image suitable for me? Here are some things to consider that will help you decide.
Launcher: In addition to text and GUI install options in the boot menu, the desktop flavors contain a launcher on the desktop that can be used to install while running the live image. Flavors: The live images come in "flavors", four providing the desktop environments GNOME, KDE, LXDE and Xfce, and two text console flavors: rescue and standard. Many users will find these initial package selections suitable, installing any additional packages they need from the network afterwards. Architecture: Only images for the two most popular architectures, 32-bit PC (i386) and 64-bit PC (amd64), are currently provided. Size: Each image is much smaller than the full set of CD/DVD images, but larger than the network install media. If you are installing from optical media, the standard and rescue images will fit on a CD, whereas the others require a DVD. If you are installing from a USB key, only LXDE, Xfce, standard and rescue will fit on a 1G device, whereas the others require a larger key. Languages: The images do not contain a complete set of language support packages. If you need input methods, fonts and supplemental language packages for your language, you'll need to install these afterwards.