[EN] Metadata - what your pictures tell about you

Also here on Steemit many own pictures and photos are uploaded. But not everyone knows what further information can be found in these pictures. Pictures can tell you more about someone than he wants to.
In this article I would like to point out which information can be stored in images and how to prevent this.

What is metadata?

In the context of metadata for images, additional information is stored in addition to the actual image information (the color values of the individual pixels).
This starts with the time of recording, goes through the camera model to GPS information, if it has been saved. These data are added to the image by the camera (or mobile phone) independently and often without the photographer's knowledge.

The Exif standard

Exif stands for Exchangeable Iimage File Fformat. Currently in version 2.31 ^[1].
The header of the image (JPEG or TIFF) also stores information on various recording parameters. The presentation and storage of this data is standardised with Exif. The following table of the german Wikipedia gives a good overview of the various attributes:

Tag-ID hex.	Tag-Name
9000	ExifVersion
010F	Make
0110	Model
0112	Orientation
9003	DateTimeOriginal
829D	FNumber
829A	ExposureTime
8833	ISOSpeed
9207	MeteringMode
013B	Artist
8298	Copyright
9286	UserComment
010e	ImageDescription

Exif is by far not the only standard used to store metadata. For example, the IPTC standard ^[2]. I don't want to go into more details here, but I wanted to introduce Exif briefly because it is probably the best known.

Practical example

My friend @maxpatternman, who brought me to this topic, kindly provided me with a photo taken by him.

There are a lot of programs that can read such metadata. For example, I use Exiftool, with which the following information can be read out:

Tag	Content
ExifTool Version Number	10.78
File Name	TESTIMG.jpeg
Directory	.
File Size	1417 kB
File Modification Date/Time	2018:02:05 14:01:26-05:00
File Access Date/Time	2018:02:05 14:01:26-05:00
File Inode Change Date/Time	2018:02:05 14:01:26-05:00
File Permissions	rw-r--r--
File Type	JPEG
File Type Extension	jpg
MIME Type	image/jpeg
Exif Byte Order	Big-endian (Motorola, MM)
Make	HTC
Camera Model Name	HTC One_M8
Orientation	Horizontal (normal)
X Resolution	72
Y Resolution	72
Resolution Unit	inches
Software	Snapseed 2.0
Modify Date	2016:09:17 01:54:32
Y Cb Cr Positioning	Centered
Exposure Time	1/100
F Number	2.0
Exposure Program	Program AE
ISO	160
Exif Version	0220
Date/Time Original	2016:09:14 10:52:48
Create Date	2016:09:14 10:52:48
Components Configuration	Y, Cb, Cr, -
Compressed Bits Per Pixel	4
Shutter Speed Value	1/100
Aperture Value	2.0
Brightness Value	2.966215
Exposure Compensation	0
Max Aperture Value	2.0
Metering Mode	Other
Light Source	Unknown
Flash	Off, Did not fire
Focal Length	3.8 mm
Sub Sec Time Original	913
Flashpix Version	0100
Color Space	sRGB
Exif Image Width	2688
Exif Image Height	1520
Interoperability Index	R98 - DCF basic file (sRGB)
Interoperability Version	0100
Custom Rendered	Normal
Exposure Mode	Auto
White Balance	Auto
Digital Zoom Ratio	undef
Focal Length In 35mm Format	0 mm
Scene Capture Type	Standard
Gain Control	None
Contrast	Normal
Saturation	Normal
Sharpness	Normal
GPS Latitude Ref	North
GPS Longitude Ref	West
GPS Altitude Ref	Above Sea Level
GPS Time Stamp	08:52:40
GPS Processing Method	ASCII
GPS Date Stamp	2016:09:14
Image Width	2688
Image Height	1520
Encoding Process	Baseline DCT, Huffman coding
Bits Per Sample	8
Color Components	3
Y Cb Cr Sub Sampling	YCbCr4:2:0 (2 2)
Aperture	2.0
GPS Altitude	569 m Above Sea Level
GPS Date/Time	2016:09:14 08:52:40Z
GPS Latitude	39 deg 51' 35.60" N
GPS Longitude	4 deg 1' 25.12" W
GPS Position	39 deg 51' 35.60" N, 4 deg 1' 25.12" W
Image Size	2688x1520
Megapixels	4.1
Shutter Speed	1/100
Date/Time Original	2016:09:14 10:52:48.913
Focal Length	3.8 mm
Light Value	8.0

What a long list. There is a lot of technical information about the recording itself and its storage.
But I now know that @maxpatternman took a photo with his HTC One M8 on 14.09.2016 at 10:52, right here:

If a photo is taken at home, the address could easily be found out. Profiles can also be created automatically for multiple images.

However, you can't rely on the metadata. It is very easy to manipulate the corresponding attributes. To counteract copyright piracy, additional steps need to be taken^[3].

How can I protect myself?

If the GPS recording setting is not enabled, it will hopefully not be written to the image. But you may also not want to share the other meta information with others.
There are a lot of online services that remove metadata, but you should be careful about this, as it is often unclear what the services do with the information.

There are certainly many tools and ways to remove the metadata. Here is just a selection

Gimp

Usually, image editing programs offer the option to delete or not save these metadata when saving the images.

With Gimp this can be achieved by removing the check mark at Save EXIF data when saving under Advanced options.

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Linux & Mac

On Linux and Mac, the above mentioned Exiftool provides the desired functionality:

exiftool -all= testimg. jpg

Besides deleting the metadata can also be manipulated with the tool ^[4] .

Windows

Under Windows, the easiest way to remove the information is as follows:

1. right click on the image -> Properties
2. click on details
3. remove characteristics and personal information
4. now you can choose whether all or only certain information should be removed -> OK

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Sources and further links

[1] http://www.cipa.jp/std/documents/e/DC-008-Translation-2016-E.pdf
Visited on 06.02.2018 11:40

[2] https://iptc.org/standards/photo-metadata/iptc-standard/
Visited on 06.02.2018 10:05

[3] http://ijrcct.org/index.php/ojs/article/viewFile/1393/pdf
Visited on 05.02.2018 23:50

[4] https://sno.phy.queensu.ca/~phil/exiftool/exiftool_pod.html
Visited on 06.02.2018 12:00

https://www.mat.ucsb.edu/Masters/Mohit_Hingorani_Web_Thesis.pdf
Visited on 06.02.2018 13:20

http://www.image-engineering.de/content/library/conference_papers/before_2009/statistic_analysis_millions_photos.pdf
Visited on 06.02.2018 13:35

In this sense, be aware of what information you want to disclose.

Thank you for reading!