You may use, copy, change and redistribute it, including in commercial and closed source work, as long as the copyright notice and permission notice stay with it. There is no warranty. It is not a copyleft licence, so it does not require you to publish your own source.
The Python Imaging Library was released by Secret Labs AB and Fredrik Lundh under what is now catalogued as the MIT-CMU licence. The notice reads, in substance:
The Python Imaging Library (PIL) is
Copyright (c) 1997-2011 by Secret Labs AB
Copyright (c) 1995-2011 by Fredrik Lundh
By obtaining, using, and/or copying this software and/or its associated
documentation, you agree that you have read, understood, and will comply
with the following terms and conditions:
Permission to use, copy, modify and distribute this software and its
documentation for any purpose and without fee is hereby granted, provided
that the above copyright notice appears in all copies, and that both that
copyright notice and this permission notice appear in supporting
documentation, and that the name of Secret Labs AB or the author not be
used in advertising or publicity pertaining to distribution of the software
without specific, written prior permission.
SECRET LABS AB AND THE AUTHOR DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS
SOFTWARE, INCLUDING ALL IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS.
IN NO EVENT SHALL SECRET LABS AB OR THE AUTHOR BE LIABLE FOR ANY SPECIAL,
INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM
LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE
OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.LICENSE file shipped with the version you are actually using, not from a web page. Pillow carries this notice at the top of its own licence file.Pillow began as a fork of PIL in 2010 and kept the licence. Its LICENSE file opens with the notice above for the original PIL code, followed by the Pillow copyright for work done since the fork. The Python Package Index lists Pillow as MIT-CMU.
In practice that means the same thing it always did: permissive, no copyleft, keep the notice, no warranty.
Yes. The licence puts no restriction on commercial use and does not require you to release your own code.
You have to keep the copyright and permission notice with copies of the software and in supporting documentation. Most projects satisfy this with a third party licences file or an acknowledgements page.
No, not without written permission. That advertising clause is the one meaningful restriction in an otherwise very open licence.
A permissive MIT style licence of this kind is generally treated as compatible with the GPL, in the sense that the combined work can be distributed under the GPL. If the answer matters to your business, ask a lawyer rather than a web page.