1. Why?
Ever since the terms and conditions fiasco with WhatsApp1, 2, the disaster that was Apple's CSAM3, I have become even more conscious about sharing images online. These images could be simple screenshots from the phone, desktop or even pictures I take on the phone or an actual camera (yes those things). The metadata that one can extract from images is beyond scary at this point. As an example, here are the parameters with filled-in values (I have Redacted a few values) from an image taken on the phone:
ExifTool Version Number : 12.44 File Name : IMG_7999.jpeg Directory : . File Size : 2.9 MB File Modification Date/Time : Redacted File Access Date/Time : Redacted File Inode Change Date/Time : Redacted File Permissions : -rw-r--r-- File Type : JPEG File Type Extension : jpg MIME Type : image/jpeg JFIF Version : 1.01 Exif Byte Order : Big-endian (Motorola, MM) Make : Apple Camera Model Name : iPhone 13 Orientation : Rotate 90 CW X Resolution : 72 Y Resolution : 72 Resolution Unit : inches Software : 15.6 Modify Date : Redacted Host Computer : iPhone 13 Tile Width : 512 Tile Length : 512 Y Cb Cr Positioning : Centered Exposure Time : 1/25 F Number : 1.6 Exposure Program : Program AE ISO : 500 Exif Version : 0232 Date/Time Original : Redacted Create Date : Redacted Offset Time : Redacted Offset Time Original : Redacted Offset Time Digitized : Redacted Components Configuration : Y, Cb, Cr, - Shutter Speed Value : 1/25 Aperture Value : 1.6 Brightness Value : -1.053634558 Exposure Compensation : 0 Metering Mode : Multi-segment Flash : Off, Did not fire Focal Length : 5.1 mm Subject Area : 2007 1505 2213 1324 Run Time Flags : Valid Run Time Value : 341412586472250 Run Time Scale : 1000000000 Run Time Epoch : 0 Acceleration Vector : 0.02649262734 -0.9928008909 -0.09302642189 Focus Distance Range : 0.10 - 1.03 m Sub Sec Time Original : 949 Sub Sec Time Digitized : 949 Flashpix Version : 0100 Color Space : Uncalibrated Exif Image Width : 4032 Exif Image Height : 3024 Sensing Method : One-chip color area Scene Type : Directly photographed Exposure Mode : Auto White Balance : Auto Focal Length In 35mm Format : 26 mm Scene Capture Type : Standard Lens Info : 1.539999962-5.1mm f/1.6-2.4 Lens Make : Apple Lens Model : iPhone 13 back dual wide camera 5.1mm f/1.6 Composite Image : General Composite Image GPS Latitude Ref : Redacted GPS Longitude Ref : Redacted GPS Altitude Ref : Redacted GPS Speed Ref : Redacted GPS Speed : Redacted GPS Img Direction Ref : Redacted GPS Img Direction : Redacted GPS Dest Bearing Ref : Redacted GPS Dest Bearing : Redacted GPS Horizontal Positioning Error: Redacted MPF Version : 0100 Number Of Images : 2 MP Image Flags : (none) MP Image Format : JPEG MP Image Type : Undefined MP Image Length : 228160 MP Image Start : 2650809 Dependent Image 1 Entry Number : 0 Dependent Image 2 Entry Number : 0 Profile CMM Type : Apple Computer Inc. Profile Version : 4.0.0 Profile Class : Display Device Profile Color Space Data : RGB Profile Connection Space : XYZ Profile Date Time : Redacted Profile File Signature : acsp Primary Platform : Apple Computer Inc. CMM Flags : Not Embedded, Independent Device Manufacturer : Apple Computer Inc. Device Model : Device Attributes : Reflective, Glossy, Positive, Color Rendering Intent : Perceptual Connection Space Illuminant : Redacted Profile Creator : Apple Computer Inc. Profile ID : Redacted Profile Description : Display P3 Profile Copyright : Copyright Apple Inc., 2022 Media White Point : 0.96419 1 0.82489 Red Matrix Column : 0.51512 0.2412 -0.00105 Green Matrix Column : 0.29198 0.69225 0.04189 Blue Matrix Column : 0.1571 0.06657 0.78407 Red Tone Reproduction Curve : (Binary data 32 bytes, use -b option to extract) Chromatic Adaptation : 1.04788 0.02292 -0.0502 0.02959 0.99048 -0.01706 -0.00923 0.01508 0.75168 Blue Tone Reproduction Curve : (Binary data 32 bytes, use -b option to extract) Green Tone Reproduction Curve : (Binary data 32 bytes, use -b option to extract) Image Width : 4032 Image Height : 3024 Encoding Process : Baseline DCT, Huffman coding Bits Per Sample : 8 Color Components : 3 Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2) Run Time Since Power Up : Redacted Aperture : 1.6 Image Size : 4032x3024 Megapixels : 12.2 Scale Factor To 35 mm Equivalent: 5.1 Shutter Speed : 1/25 Create Date : Redacted Date/Time Original : Redacted Modify Date : Redacted GPS Altitude : Redacted GPS Latitude : Redacted GPS Longitude : Redacted MP Image 2 : (Binary data 228160 bytes, use -b option to extract) Circle Of Confusion : 0.006 mm Field Of View : 69.4 deg Focal Length : 5.1 mm (35 mm equivalent: 26.0 mm) GPS Position : Redacted Hyperfocal Distance : 2.76 m Light Value : 3.7 Lens ID : iPhone 13 back dual wide camera 5.1mm f/1.6
A wonderful new site by Lennart Ziburski titled "Rehthinking how technology uses our personal data" visually explores how keeping our data and AI on on-device could empower users. However, an angle that is missing in the article is even the need for some of this data to be collected in the first place. Do we really need it collected? Do we need this data to add value to our lives? One can argue some of these devices and apps allow users to customize or even minimize the amount of data collected (for pictures at least).
2. So what now?
This does mean that it becomes important to figure out ways to scrub out the metadata that is available on these pictures. That is where the wonderful world of FOSS came in and the users on Fosstodon pointed me to ExifTool. As described on it's website, ExifTool is a platform-independent Perl library plus a command-line application for reading, writing and editing meta information in a wide variety of files…. This was precisely what I needed for myself.Not only does it allow for scrubbing metadata, it allows us to modify them and add new custom user-defined tags.
3. Usage and examples
Viewing metadata: As simple as passing the filename to ExifTool.
exiftool IMGNAME
Scrubbing: Fairly straightforward to remove all metadata from an image. The command below allows you to remove all metadata from the image. Please note that without using the -overwriteoriginal, a new file is created.
exiftool -all= -overwrite_original IMGNAME
Here is the text from man,
-overwrite_original Overwrite the original FILE (instead of preserving it by adding "_original" to the file name) when writing information to an image. Caution: This option should only be used if you already have separate backup copies of your image files. The overwrite is implemented by renaming a temporary file to replace the original. This deletes the original file and replaces it with the edited version in a single operation. When combined with -o, this option causes the original file to be deleted if the output file was successfully written (ie. the file is moved instead of copied).Selectively writing specific tags: In my use-case, I need to specifically add CC licensing details to my image as I have decided to share all my images with those licenses. the example to do so is fairly simple.
exiftool -overwrite_original -XMP-cc:license="http://creativecommons.org/licenses/by-sa/4.0/" -XMP-cc:AttributionName="" -XMP-cc:AttributionURL="" -xmp:usageterms="This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License http://creativecommons.org/licenses/by-sa/4.0/"
This allows me to share an image with these terms and they pop-up whenever anyone views them with any metadata tool across the board.