These components are licensed under proprietary terms, incompatible with the GPL and similar licenses.
However, the Fiji project has obtained permission to distribute them as part of its distribution:
Date: Mon, 26 Jul 2010 10:58:20 +0200 From: Michael Unser <email@example.com> [...] we are happy that Fiji distributes our software: you have my formal authorization for this (in my quality of lab chief). "You'll be free to use this software for research purposes, but you must not transmit and distribute it without our consent": this means that from now on, you are authorized to distribute any ImageJ pluging listed at http://bigwww.epfl.ch/algorithms.html since you have our consent.
See the Fiji LICENSES file for details.
List of BIG components
The following components are expressly or implicitly licensed this way: