Preservation of Metadata



What is Metadata?

Metadata is "data about data". For example when you take a photograph using a phone or a digital camera the make and model of the camera, the date and time the photo was taken, the exposure time, etc. will normally be stored within the JPG file in a format known as EXIF data. When you view the photo on your phone or computer you would normally initially see the photo itself but (depending what app you are using to view it) you will be able to select a "file information" or "properties" option which will display that metadata.


Different types of metadata     

EXIF data is only one example of metadata. Other file types may have metadata in other forms. In additional all files of all types will normally have a "date modified" date/time.


Preserving Metadata  

It is important to preserve, so far as possible, the metadata of files when copies are taken. Exactly how to do this will depend on on the particular computer systems involved, and you may need to seek specialist advice, but some factors which you may wish to consider are discussed below. When considering the discussion below of methods which generally do, or generally do not, preserve particular kinds of metadata, bear in mind that new versions of apps may treat metadata differently, and also that the version of an app supplied for one platform may differ in this respect from a version of the same app on a different platform.


Windows Explorer

If you have files on an Android device you can plug it in to the USB socket on a Windows computer and copy files using Windows Explorer. Generally Windows Explorer does preserve metadata included date-modified time/date. 

Note that it is possible to plug an Apple device into the USB socket on a Windows computer but generally this is of little practical use because (a) the Apple device normally only provides visibility to photo files on the device and (b) the Apple device strips off EXIF data when a file is transferred.


Cloud storage                

If you upload files to a cloud storage system and download them from the cloud storage system to another device, most cloud storage systems will preserve metadata internal to the file - such as EXIF data - but will not preserve the date-modified date/time. However MEGA appears to preserve both internal metadata and "date modified" metadata.  


Sending files by file transfer

There are a number of file transfer websites including FileMail which are designed to allow you to transfer large files quickly. The files are loaded up to the website and a temporary link is provided so that they can be downloaded on any device. Most file transfer systems will preserve metadata internal to the file - such as EXIF data - but will not preserve the "date modified" date/time. 


Sending files as email attachments

If you send a file as an attachment to an email you might expect that when it is received and downloaded the file's metadata will be unchanged. But this is often not the case. First of all, it is unlikely that the date-modified date/time will be preserved. Normally the attached file, as downloaded by the recipient, will have a date-modified which is the date of downloading. Often metadata which is actually within the file - such as EXIF data - should be preserved, but even this is not always the case. Apple devices, in particular, are prone to strip off EXIF data when an image file is sent by email.

One way of trying to prevent this loss of metadata, when sending files as email attachments, is to save the files into a ZIP file and then send the ZIP file as an email attachment. The original idea of ZIP files is that they store the data in compressed form to save transmission time. A very simple example of how compression works is that a file might contain 90 space characters in a row and this could be compressed into a single space character accompanied by a special character to indicate the the character is repeated and the number 90. So what was 90 bytes becomes just a few bytes. Having been transmitted from one device to another the compressed data can then be uncompressed so that it is the same as it originally was. Although the original idea of compressing files is to save transmission time, one side effect of sending any files attached to emails in ZIP format is that the metadata of the compressed files should be preserved because any process which might, for example, have stripped off EXIF data from JPG files will not operate because it will not recognise the files in their compressed format. However ZIPing files will not prevent the "date modified" time/date being lost.


Lossy compression 

ZIP files are an example of lossless compression where the compression/decompression process does not result in any loss of data (although it does result in the loss of "date modified" metadata). Lossy compression is where some data is actually lost. One common use of lossy compression is for photographs. Many digital photos have a very large number of pixels and the number of pixels can be reduced with only minimal apparent loss of picture quality. For legal proceedings, however, it is important that the original file should be preserved so it is important to make sure no file is subject to a lossy compression process. Systems such as Google Photos should be avoided because they compress photos.



Disclaimer

This information page is designed to be used only by clients of John Antell who have entered into, or are about to enter into, an agreement for the provision of legal services. The information in it is necessarily of a general nature and is intended to be used only in conjunction with specific advice to the individual client about the individual case. This information page should not be used by, or relied on, by anyone else.

The information on this page about specific computer techniques is provided for information purposes only. Every reasonable effort has been made to ensure that the information is accurate and up to date at the time it was written but no responsibility for its accuracy, or for any consequences of relying on it, is assumed by me. You should satisfy yourself, before using any of the techniques, software or services described, that the techniques are appropriate for your purposes and that the software or service is reliable.


This page was lasted updated in November 2019. Disclaimer