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documented exif filtering
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ralsina committed Jul 19, 2016
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Expand Up @@ -1435,6 +1435,81 @@ be stripped. For example ``03_an_amazing_sunrise.jpg`` will be render as *An ama
Here is a `demo gallery </galleries/demo>`_ of historic, public domain Nikola
Tesla pictures taken from `this site <>`_.

Handling EXIF Data

Your images contain a certain amount of extra data besides the image itself,
called the `EXIF metadata. <>`__
It contains information about the camera you used to take the picture, when it was taken,
and maybe even the location where it was taken.

This is both useful, because you can use it in some apps to locate all the pictures taken
in a certain place, or with a certain camera, but also, since the pictures Nikola
publishes are visible to anyone on the Internet, a privacy risk worth considering
(Imagine if you post pictures taken at home with GPS info, you are publishing your
home address!)

Nikola has some support for managing it, so let's go through a few scenarios to
see which one you prefer.

Strip all EXIF data

Do this if you want to be absolutely sure that no sensitive information should ever leak::


Preserve all EXIF data

Do this if you really don't mind people knowing where pictures were taken, or camera settings.

EXIF_WHITELIST = {'*': '*'}

Preserve some EXIF data

Do this if you really know what you are doing. EXIF data comes separated in a few IFD blocks.
The most common ones are:

Information about the image itself, and camera settings

Information about embedded thumbnails (usually nothing)

An embedded thumbnail (usually nothing)

Geolocation information about the image

Not too interesting at this point.

Each IFD in turn contains a number of tags. For example, 0th contains a ImageWidth tag.
You can tell Nikola exactly which IFDs to keep, and within each IFD, which tags to keep,
using the EXIF_WHITELIST option.

Let's see an example::

"0th": ["Orientation", "ImageWidth", "ImageLength"],
"Interop": "*",

So, we preserve EXIF data, and the whitelisted IFDs are "0th" and "Interop". That means
GPS, for example, will be totally deleted.

Then, for the Interop IFD, we keep everything, and for the 0th IFD we only keep three tags,
listed there.

There is a huge number of EXIF tags, described in `the standard <>`__

Post Processing Filters

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