Debian

The standard CD images are built by Copyleft using the Debian CD package without modification. This includes checking the mirror, md5sums and dependencies of each package and md5sums are included on the discs themselves.

From time to time Enhanced disc sets are produced using modified scripts from the Debian CD package. Again each package has its md5sum and dependencies checked and md5sums are included on the discs. I know these scripts well and what can be done with them.
The DVD is basically an enlarged CD.

The Standard and Enhanced sets are burnt from file-trees using a genisoimage | wodim pipe.

The Copyleft Official Debian images are produced from the Copyleft archive using the official jigdo files. The discs are burnt from these images. Historically the Official CD images have lagged behind the official ftp mirrors.

Fedora, Mandriva, CentOS and Smeserver use the Red Hat(tm) packaging system which means that they often can install each other's binary .rpm packages.

Slackware is the oldest surviving distribution and uses tar files to install its packages. Yoper uses its own installation method.

Ubuntu, Knoppix uses the Debian packaging system which means that it can install .deb packages, but be careful!! It is not advisable to convert from these distributions to Debian.

Non-Debian distributions are downloaded as iso images and the md5sums checked. On occasion an iso image has been rebuilt because of some problem, or to incorporate some feature, typically updates.