Manipulating stored geocoordinates in cellphone photos
exiftool to the Rescue
Although there is a go-exif2 library for Go which reads Exif tags, there is no easy-to-use library that writes new tags or refreshes the existing tags in a JPEG file. This is why Listing 1 resorts to the Unix utility exiftool
. On Ubuntu, this jack-of-all-trades can be set up via the package manager (Listing 5, first line). The tool expects coordinates in a floating-point format and either creates or refreshes the corresponding Exif tags in a JPEG image file (second line).
Listing 5
Editing Exif Tags
01 $ sudo apt-get install exiftool 02 $ exiftool -gpslatitude=37.<xx> -gpslongitude=-122.<yy> file.jpg
The patch()
function from line 42 of Listing 1 calls the tool from Go via the os/exec
interface. It takes the name of a program including parameters. To collect the output of the command-line utility invoked, programmers provide a byte buffer, assigned to the Stdout
and Stderr
outputs. Run()
starting in line 52 invokes the external process, grabs its output, and checks the exit code.
Normally, exiftool
returns with an exit code of
. In this case, the error err
in line 53 is equal to nil
, and patch()
returns to the caller (the main program) after the work is done. exiftool
modifies the JPEG file given to it directly and stores a backup of the original in x_original
, but geofuzz
is not interested in this, and therefore simply ignores it, leaving it in the same directory.
To generate an executable geofuzz
binary from the source code in Listing 1, Listing 6 shows the Go commands for initializing a Go module and compiling the code while automatically downloading any dependencies from GitHub. Then you just need to install geofuzz
in a path listed in your PATH
variable, and a quick call to geofuzz file.jpg
quickly drops a privacy-friendly obfuscation layer over the geotags in the file. Curious online snoopers will be furious, because they'll be searching in the wrong part of town!
Listing 6
Generating the Binary
01 $ go mod init geofuzz 02 $ go build geofuzz.go
Infos
- Exif format: https://en.wikipedia.org/wiki/EXIF
- GeoImgr: https://tool.geoimgr.com
- "Programming Snapshot: Go program finds photos with nearby GPS coordinates," by Mike Schilli, Linux Magazine, issue 225, August 2019, p. 44, https://www.linux-magazine.com/Issues/2019/225/Programming-Snapshot-Go/(language)/eng-US
- Generating random locations nearby?: https://gis.stackexchange.com/questions/25877/generating-random-locations-nearby
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