Underscan Published on February 28, 2008
by Underscan

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Removing "sensitive" meta data using ExifTool

Thursday February 28, 2008 at 01:08PM

As Ipernity extracts Exif meta data to a great extent, i. e. not only "basic" information such as exposure, aperture, creation dates, etc., but really almost "all that's there" and I am usually very privacy-aware and "data-economical", that is an aspect I have been sort of uncomfortable with.
Especially data such as the Serial Number of the camera and other "sensitive" meta data that could easily be used to trace back to an individual - and are of hardly any use for other purposes such as figuring out the method of shooting - caught my attention.

[On a sidenote to kind of fend off speculations of paranoia on my part: last year Canon announced it would be potentially possible to track down the person who had photographed/-copied the latest Harry Potter novel by means of the meta data of the camera used, cf. Times Online]

Of course you can disable displaying Exif data but I do want to let others interested in exposure or ISO easily have access to this information. So disabling display of Exif all together is no option for me.
The only solution thus is to remove all IMO "unnecessary" meta data from the files before uploading them.

Here is what I have figured out for myself so far, I might overhaul it in the future since it is rather rudimentary - but sufficient - at the moment.

I decided to use ExifTool, which is
a platform-independent Perl library plus a command-line application for reading, writing and editing meta information in image, audio and video files.

It is a very powerful and flexible tool that can do a lot more than what I use it for - e. g. also handle meta data from other file types than images.

At the moment I have decided to do the following with it:

  1. exiftool -all= *.jpg
    This removes all meta data from all files ending with the extension .jpg in the current folder, moving the originals to files with the additional extension "_original".
  2. exiftool -overwrite_original -tagsfromfile *_original -make -model -exposuretime -aperturevalue -flash -iso -lens -focallength -orientation -datetimeoriginal *.jpg

    This copies the specified meta data (Make, Model, Exposure, etc.) from the "backuped" _original files to those stripped clean of any data.

Of course the fields can be extended or reduced to everyone's personal needs and the whole thing put into a nice shell script etc.

I still need to figure out what information is stored by my camera in what fields and what groups - it's well documented but rather complex - so I can specify more precisely what data to copy.

As I wrote above, this solution is rather rudimentary and not perfected, since e. g. certain fields (e. g. Components Configuration: YCbCr) are created - I assume because of interdependence with other fields/groups and meta data specifications -, but functional for the moment and a better solution for me to either shutting off the display of Exif data completely or showing everything.

3 Comments / add your comment?

Christophe says:
I totally agree.
Posted 21 months ago. ( permalink )
Chris82pro says:
Very good post :-) I agree about this. It's not necessary that any Photoshop IDs and/or Serials are shown, maybe we should contact the Ipernity team about this. It should be easily possible to display only certain informations like ISO and aperture settings. When downloading a pic the EXIF would still be there, but at least it would reduce the amount of data freely available quite a bit already.
Posted 21 months ago. ( permalink )
Underscan replies:
maybe we should contact the Ipernity team about this. It should be easily possible to display only certain informations like ISO and aperture settings.

Indeed that would probably be easy. I actually assume that the ExifTool Perl library I described is being used for extraction of the meta data.

Although I personally would be an advocate of a generally reduced display of meta data, esp. that which makes users "trackable", I believe it should be everyone's own decision what to show and what to hide.
It would be hard, if not impossible, to satisfy every member when choosing which fields to display. Some may want to let others know colour temperature and levels while others would want to hide the focal length or their camera model.
I thus doubt a "general rule from above" would be of much use other than cause commotion.

It is a good thing you can already choose if you want to have the Exif data displayed at all. That might make some people think.

All in all I can't see a better solution other than trying to get people to be aware of the ("invisible") information they might disclose when uploading files.

It would be super-nice of course if e. g. you could edit Exif data via the jUploadr which already has
Enhanced EXIF support: jUploadr now reads EXIF caption, headline and geo tags, and adds the appropriate information
So you could remove fields right before uploading when adding title etc.
Unfortunately I don't think such a feature would be high on the coders' priority list.
Posted 21 months ago. ( permalink )

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