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.


The best way of preserving Metadata when copying files?  

It is important to preserve 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 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. So do double-check that if you use any of the three methods below to copy files that metadata is preserved in the copy. Pay particular attention to preservation of the file "date modified" metadata - many methods of copying files preserve internal metadata but not the file "date modified" metadata

The main methods (that I am aware of) of copying files which normally should preserve metadata including, crucially, file "date modified" metadata, are 

1. Compressing the documents into a ZIP file, sending that ZIP file by email, and then unZIPing on the target system using an unZip program such as 7-ZIP (not the WIndows built-in UnZIP).

2. Copying the file to a USB drive or SDcard and then inserting the drive/card into the target device and copying the file from the drive/card onto the target device.

3. Using a USB cable to connect an Android device to a Windows computer and using Windows Explorer to copy files.


For a more general discussion of the pros and cons of various methods of copying files from one device to another, see below.


Various methods and their pros and cons

Windows Explorer and Android

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. 


Cloud storage                

If you upload files to a general cloud storage system and download them from the cloud storage system on 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, at the time of writing, MEGA and pCloud appear to preserve both internal metadata and "date modified" metadata. You need to be aware of the privacy implications of using the internet


Legal Document Management systems 

If you load a document to Bundledocs and then download it, metadata internal to the file - such as EXIF data - is preserved but date-modified date/time is not preserved - Bundledocs very usefully uses date-modified metadata to set the document date withing the Bundledocs system when loading a document but date-modified metadata is not preserved in copies of files as subsequently downloaded. You need to be aware of the privacy implications of using the internet   


Sending files by file transfer

There are a number of file transfer websites 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. You need to be aware of the privacy implications of using the internet


Sending files as email attachments

The standard format for sending emails and attachments over the internet (known as MIME) has a field for the "date modified" date/time of each attached file. However not all email clients correctly make use of this field. Most email clients will fill in the "date modified" field correctly when sending an email with attachments but many email systems ignore the field when processing received emails so that when an attachment is saved on the receiving device it is given a "date modified" date/time which is the date/time of the email itself (or even the later date/time when the attachment is saved) not the original date/time for that attachment from MIME. With regard to other metadata, metadata which is actually within the attached file - such as EXIF data - will usually be preserved, but even this is not always the case. Apple systems, in particular, are prone to strip off EXIF data when an image file is sent by email.

One way 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 was 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. However you should take care that the UnZIP program you use to uncompress the files does restore the original "date modified" dates of the files when uncompressing them. 7-ZIP should do this but the built-in Windows UnZIP, for example, does not.

You need to be aware of the privacy implications of using the internet  


Lossy compression 

ZIP files are an example of lossless compression where the compression/decompression process does not result in any loss of data. Lossy compression, on the other hand, 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 do a lossy compression of photos (actually Google Photos itself does have an option not to do lossy compression but even if you select that option it still does not preserve "date modified" metadata and so should not be used for copying files for that reason).



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 July 2020. Disclaimer