EXIF metadata
Posted on Feb 14 - 2021
All information hidden in a photo
Photos can contain a lot of information, some even sensitive such as the device with which you took the photo, information on the software used, date and time, and even GPS coordinates. So when you send a photo, you have to take into account that all this information can eventually be extracted and read by whoever has the photo.
Index
Exif
Exif is a specification for the image file format and takes care of adding to your photos a list of information like the ones written above. However, the Exif isn’t present in any image, it depends on the format of the photo. The Exif covers formats like JPEG (.jpg / .jpeg / .jpe / .jif / .jfif / .jfi) and others less used. For example .gif does not support Exif while PNG formats have been updated to support it.
To better understand this, the Exif of a photo taken at the Apple Store in Milan, Italy:
File Name : AppleStore.jpg
Directory : .
File Size : 2439411
File Modification Date/Time : 2021:02:14 12:24:36+01:00
File Access Date/Time : 2021:02:14 12:58:28+01:00
File Inode Change Date/Time : 2021:02:14 12:58:26+01:00
File Permissions : 644
File Type : JPEG
File Type Extension : JPG
MIME Type : image/jpeg
JFIF Version : 1 1
Exif Byte Order : MM
Make : Apple
Camera Model Name : iPhone SE
Orientation : 3
X Resolution : 72
Y Resolution : 72
Resolution Unit : 2
Software : 12.1
Modify Date : 2018:12:26 12:31:05
Exposure Time : 0.005128205128
F Number : 2.2
Exposure Program : 2
ISO : 25
Exif Version : 0221
Date/Time Original : 2018:12:26 12:31:05
Create Date : 2018:12:26 12:31:05
Components Configuration : 1 2 3 0
Shutter Speed Value : 0.00512500000015632
Aperture Value : 2.20000000038133
Brightness Value : 7.783494385
Exposure Compensation : 0
Metering Mode : 5
Flash : 24
Focal Length : 4.15
Subject Area : 2015 1511 2217 1330
Run Time Flags : 1
Run Time Value : 1333242986804375
Run Time Scale : 1000000000
Run Time Epoch : 0
Acceleration Vector : 1.000010014 0.02013684064 -0.07763625681
Sub Sec Time Original : 704
Sub Sec Time Digitized : 704
Flashpix Version : 0100
Color Space : 1
Exif Image Width : 4032
Exif Image Height : 3024
Sensing Method : 2
Scene Type : 1
Exposure Mode : 0
White Balance : 0
Focal Length In 35mm Format : 29
Scene Capture Type : 0
Image Unique ID : 5b0091944220618c0000000000000000
Lens Info : 4.150000095 4.150000095 2.2 2.2
Lens Make : Apple
Lens Model : iPhone SE back camera 4.15mm f/2.2
GPS Latitude Ref : N
GPS Longitude Ref : E
GPS Horizontal Positioning Error: 0
Current IPTC Digest : cc870bf9ec6673116d7f0a3ace305e88
Coded Character Set : .%G
Application Record Version : 2
Digital Creation Time : 12:31:05
Digital Creation Date : 2018:12:26
Date Created : 2018:12:26
Time Created : 12:31:05
IPTC Digest : cc870bf9ec6673116d7f0a3ace305e88
Image Width : 4032
Image Height : 3024
Encoding Process : 0
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : 2 2
Run Time Since Power Up : 1333242.98680437
Aperture : 2.2
Image Size : 4032 3024
Lens ID : iPhone SE back camera 4.15mm f/2.2
Megapixels : 12.192768
Scale Factor To 35 mm Equivalent: 6.98795180722891
Shutter Speed : 0.005128205128
Create Date : 2018:12:26 12:31:05.704
Date/Time Original : 2018:12:26 12:31:05.704
GPS Latitude : 45.4654583333333
GPS Longitude : 9.19410277777778
Date/Time Created : 2018:12:26 12:31:05
Digital Creation Date/Time : 2018:12:26 12:31:05
Circle Of Confusion : 0.00429972350378608
Field Of View : 63.6549469203797
Focal Length : 29
GPS Position : 45.4654583333333 9.19410277777778
Hyperfocal Distance : 1.8206773258829
Light Value : 11.8823373613072
If use GPS location information we get the precise point where the photo was taken:
Problem
As already mentioned, there may be some sensitive information that in certain situations it’s better not to share.
A trivial example, but certainly the most frequent in this period, is to share your photos with people you have just met. By always leveraging location information, a person can track where you are, where you live, and more.
From the date and time the photo was created, can check whether you were present in a certain place or not; or verify that you haven’t modified the photo to alter the data.
Or a company can catalog the set of EXIFs present in the photos to obtain geographic or global information for advertising purposes, if in one place 90% of the photos are taken by an Apple device then the company will bring advertisers to incentivize the purchase of Apple products in that area.
Even information on the device used can be seen as an important or not “feature”.
Solution
Usually, applications or software that allow you to send multimedia files (WhatsApp, Telegram, email, Bluetooth sharing, and many others) automatically delete what’s in the EXIF.
For example, Telegram allows you to send a photo in two ways: compressed or original (without any compression). In the first case, the EXIF eliminated sensitive information, in the second case the EXIF remains intact.
The solution is, of course, delete any data before sending certain photos. Various tools allow you to do this such as ExifTool.
Using the command line, you get all the information in the EXIF:
exiftool -n /path/to/image.jpg
Or delete them entirely:
exiftool -all= /path/to/image.jpg
Trying this last command on the photo above, this’s the only information you get:
ExifTool Version Number : 12.00
File Name : AppleStore.jpg
Directory : .
File Size : 2437427
File Modification Date/Time : 2021:02:14 18:22:22+01:00
File Access Date/Time : 2021:02:14 18:22:24+01:00
File Inode Change Date/Time : 2021:02:14 18:22:22+01:00
File Permissions : 644
File Type : JPEG
File Type Extension : JPG
MIME Type : image/jpeg
Image Width : 4032
Image Height : 3024
Encoding Process : 0
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : 2 2
Image Size : 4032 3024
Megapixels : 12.192768