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Introducing JpegWasher
======================

Executive Summary
-----------------

This program makes it easy to remove metadata from the digital images
you create.

What is “Metadata” and Why Would I Want to Remove It?
-----------------------------------------------------

You may not realize it, but image files can (and typically do!) contain
more than just image data. These data can include your camera make,
model, and serial number; the location where you took the photo; the
software you used to edit the photo (and what editing steps you did);
etc.

One of the most powerful uses of photography is to graphically document
things that the wealthy and powerful might wish to remain concealed. The
evils of slavery, child labor, poverty, war, and imperialism have all
been documented photographically, and such photographs have often proved
instrumental in helping to motivate social change.

Because of the metadata they contain, digital photographs contain data
which has been used to determine who took them, and in some cases to
exact retribution against those photographers. JpegWasher makes it easy
to see and remove the privacy-compromising metadata in your images.

Even if your images are not of such a sensitive nature, that extra data
takes up space. It is not uncommon for a 100 KiB image to contain 20 KiB
of metadata in it; if that image is on a web page, that makes for 20 KiB
of wasted network usage each time the image is sent.

What Makes JpegWasher Different from Other Metadata Editors?
------------------------------------------------------------

Simply put, it is designed to *safely* remove *unimportant* metadata
from JPEG files.

There are plenty of general-purpose image metadata editors out there,
and these tools can be employed to remove unimportant metadata. The
trouble is, they are not user-friendly: it is up to you, the user, to
know which metadata are unimportant, and to delete it.

There can be literally *hundreds* of bits of metadata in an image, and
*not all are safe to remove*. In particular, if you accidentally remove
color-management metadata, computers that don’t handle images without
color-management metadata properly (I’m talking about *you*, Apple
Computer, Inc.) will display colors that often look all “washed-out” or
otherwise incorrect.

Likewise, there are already plenty of simple-to-use, user-friendly tools
out there for cleaning the metadata out of image files, but they
inevitably delete *all* metadata, resulting in files that often display
improperly. Also of concern, many of these “tools” are actually online
services. If you’re concerned about your privacy, why would you trust
the images you’re processing to some unknown third party, who may be
linked somehow to those who might want to retaliate against you?

I wrote this program because I wanted there to be a quick, easy way to
scrub images before they even left a photographer’s computer and made
their way onto the Internet, and for that program to leave vital
metadata alone, so that the resulting images continue to display
properly.

JpegWasher Washes More than Just Exif Metadata
----------------------------------------------

Jpeg is the most common type of metadata, but image files commonly
contain compromising XMP or IPTC data, particularly if they have been
edited with a tool like Photoshop. JpegWasher will seamlessly deal with
these kinds of metadata, too. It tries to do as thorough a job as
possible of scrubbing possibly compromising metadata from your images.

Using JpegWasher
----------------

Just double-click on the JpegWasher icon and a main window should open
up. Either choose the File… Wash from the menu bar, or just drag image
files onto the main JpegWasher image.

When JpegWasher opens an image, it displays all the metadata it finds.
That metadata will be run through an internal whitelist, and any data
whose “key” is not found on the whitelist will be automatically selected
for deletion.

If you disagree with JpegWasher’s decisions, you can check or uncheck
the boxes next to the metadata in question. When you are satisfied with
the choice of metadata to be scrubbed, click “Wash” and all offending
metadata will be removed. A dialog will pop up showing the metadata
remaining in the new, washed file.

Important: Run JpegWasher Last!
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Most image-editing tools insert telltale bits of metadata into the
output they create. Thus, only way you can create a file with the
minimum amount of metadata in it is to run JpegWasher as the final step
in your image preparation.

Washing Non-JPEG Images
~~~~~~~~~~~~~~~~~~~~~~~

In short: it’s possible, but it is not recommended unless you *really*
know what you’re doing.

JpegWasher is called JpegWasher for a reason: it is geared to cleaning
metadata in *JPEG* files. Different types of images use metadata
differently; metadata that would be extraneous deadwood in a JPEG can be
critical to interpreting other image file formats correctly.
JpegWasher’s built-in whitelist is geared to what must be retained when
washing JPEG images, so *careless use of JpegWasher is likely to damage
non-JPEG files.* It is for this reason that JpegWasher will warn you if
you attempt to open and wash a non-JPEG file with it.

Output Files
------------

JpegWasher never modifies an existing image file. Instead, it creates a
new file of the same type but with “_washed” appended to its name. For
example, processing ``foo.jpg`` will create ``foo_washed.jpg``. By
default, the new file will be created in the same directory as the file
being washed.

JpegWasher is Configurable
--------------------------

Both the whitelist and the destination directory for the washed files
are user-configurable in the Preferences menu.

Configuring the Whitelist
~~~~~~~~~~~~~~~~~~~~~~~~~

There are two kinds of whitelist entries: those that match an entire
metadata key, and those that match a key prefix. The latter end in an
asterisk. The whitelist is case-sensitive; i.e. the entry
``exif.image.colormap`` *will not* match the ``Exif.Image.ColorMap``
key.

That’s about It
---------------

JpegWasher does not, and probably never will, do anything but remove
extraneous metadata from JPEG files.

First, I have no desire to re-invent the wheel. There are already
excellent open-source tools like Gimp for image editing, and ExifTool
and Exiv2 for general-purpose metadata editing (in fact, JpegWasher is
built on top of Exiv2). If you need the functionality of some other
tool, download and use it!

Second (and more importantly), I want JpegWasher to be simple, and
therefore easy to learn and easy to use. The more challenging an
information-security tool is to use, the less likely it is to be used
frequently, and the more likely it is that compromising information gets
disclosed.