Welcome to all the new subscribers to this mailing list. :-)
A few recent policy updates:
The practice of overwriting images with red crosses when a "superior"
version is available is to be considered deprecated. In other words:
please don't do it anymore.
Please only delete redundant files if they are no longer in use
anywhere in Wikimedia. Use the "check usage" tab on the file
description page to do so. For the PNG=>SVG transition, tagging
obsolete PNGs with [[Template:SupersededSVG]] is preferable to
deleting or overwriting old images.
Overwriting files by someone else should be done with extreme caution,
especially if the file is in use in Wikimedia. In most cases, it will
be preferable to upload an alternative version, and point people to
it. Many photographers understandably do not appreciate it if their
work is substantially altered -- even more so, if that alteration is
made on Commons and silently propagates to a project that uses the
photo.
That is not to say that the "wiki principle" of editing does not apply
to images and other media files. Consensus and caution are just much
more advisable here due to the crossing of project and language
barriers.
There has been a lot of recent tension between users from other
projects, and Commons admins, and I hope that these changes will
improve cross-project cooperation.
Arnomane and Duesentrieb have been working on updating the Deletion Guidelines:
http://commons.wikimedia.org/w/index.php?title=Commons:Deletion_guidelines&…
There is also ongoing discussion about these issues on the Village Pump:
http://commons.wikimedia.org/wiki/Commons:Village_pump
Best,
Erik