The Data Behind the Photo

March 31, 2011 | Blog,Privacy | Matt | 2 Comments

I’ve been thinking about sharing more photos online via Twitter and Facebook but was curious what information was actually being shared when I uploaded a picture. I’ve done some sleuthing and it turns out the answer is a lot.

Similar to a webpage having source code (and metadata) a picture also has the same information attached, generally in EXIF format. This information can contain the “who, what, where, and when” details of your photo. When you upload your picture to email (i.e. Gmail, Hotmail), a social network (Facebook, Twitter) or any photo sharing service (SmugMug, Flickr, Posterous) the metadata is most likely NOT being removed. This means that anyone with access to your photo can use a simple, free program like ExifTool to extract data about your picture. Example of full extract is below.

While you might not care if SmugMug knows which devices you have (I don’t) it could potentially be exploited for advertising (or something malicious). SmugMug, for example (who I love), could send me a reminder that my iPhone 4 may be up for a discounted upgrade after two years. They know my device and how long I’ve been using it, after all. This data something you might want to consider before upload pictures of your favorite spot, your vacation house, or your kids online.

Example Exif metadata

(*taken from my friend, Pete’s, file) with bolding added for emphasis.

ExifTool Version Number : 8.53
*Profile Creator : Null
*Profile ID : 29f83ddeaff255ae0000xxxx0000xxxx
File Name : photo 2.JPG
Directory : C:/Users/matt.solar/../exiftool-8.53
File Size : 1471 kB
File Modification Date/Time : 2011:03:31 13:57:17-04:00
File Permissions : rw-rw-rw-
File Type : JPEG
MIME Type : image/jpeg
Exif Byte Order : Big-endian (Motorola, MM)
Make : Apple
Camera Model Name : iPhone 4
Orientation : Horizontal (normal)
X Resolution : 72
Y Resolution : 72
Resolution Unit : inches
Software : 4.2.1
Modify Date : 2011:03:31 08:32:28
Y Cb Cr Positioning : Centered
Exposure Time : 1/331
F Number : 2.8
Exposure Program : Program AE
ISO : 80
Exif Version : 0221
Date/Time Original : 2011:03:31 08:32:28
Create Date : 2011:03:31 08:32:28
Components Configuration : Y, Cb, Cr, –
Shutter Speed Value : 1/331
Aperture Value : 2.8
Metering Mode : Average
Flash : Off, Did not fire
Focal Length : 3.9 mm
Subject Area : 1295 967 699 696
Flashpix Version : 0100
Color Space : sRGB
Exif Image Width : 2592
Exif Image Height : 1936
Sensing Method : One-chip color area
Exposure Mode : Auto
White Balance : Auto
Scene Capture Type : Standard
Sharpness : Hard
GPS Latitude Ref : North
GPS Longitude Ref : West
GPS Altitude Ref : Above Sea Level
GPS Time Stamp : 12:32:27.16
GPS Img Direction Ref : True North
GPS Img Direction : 1.556945781
Compression : JPEG (old-style)
Thumbnail Offset : 882
Thumbnail Length : 6213
Image Width : 2592
Image Height : 1936
Encoding Process : Baseline DCT, Huffman coding
Bits Per Sample : 8
Color Components : 3
Y Cb Cr Sub Sampling : YCbCr4:2:0 (2 2)
Aperture : 2.8
GPS Altitude : 26 m Above Sea Level
GPS Latitude : 42 deg 20′ 22.20″ N
GPS Longitude : 71 deg 20′ 41.40″ W
GPS Position : 42 deg 20′ 22.20″ N, 71 deg 20′ 41.40″ W
Image Size : 2592×1936
Shutter Speed : 1/331
Thumbnail Image : (Binary data 6213 bytes, use -b option to extract)
Focal Length : 3.9 mm
Light Value : 11.7

Additional resources:

ExifTool
Wiki details for ExifTool
Privacy and GeoTagging Photos with GPS-enabled iPhone
Wikipedia details on Geotagging

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Peter Kuhn

http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=exif+data+app

looks like many apps screw up exif
Matt Solar

It *sounds like* Posterous keeps the Exif data for their use but strips it from the public-facing file: http://forums.posterous.com/exif-data-in-pictures

I’d love to hear if anyone knows for sure which services, if any, remove Exif data.