For normal use we recommend installing TeX Live over the Internet or from DVD, but if you want to burn your own DVD, you may want to get our huge ISO image. It is around 2GB (md5, sha256 checksums). You can:
If you want to mount the image to make the contents available for
installation or browsing, a typical invocation on Unix is:
mount -t iso9660 -o ro,loop,noauto /your/texlive2013.iso /mnt
On Windows, you'll need third-party tools such as daemon-tools or Magic ISO.
After mounting the image, to install TeX Live, follow the installation instructions or read the documentation, which has a section on ISO installation.
The ISO image is not updated after release; it is meant to serve as a stable marker in TeX development and to correspond to the DVD sent to TeX user group members.
Information about other ways to acquire TeX Live is available separately.