John Q. Public has just finished importing the videos and pictures from the digital camera to his laptop but realizes that the media files are incorrectly time-stamped.

Maybe the date and time settings of his “point and shoot” camera were set incorrectly or maybe the digital camera was stamping the files with local time though the pictures were being shot in another country with a different time zone. He probably forgot to change the time stamp of the camera before going on vacation.

How does John change the data and time of his pictures?

Most image editing software, Picasa and iPhoto included, allow you corect the data and time of photographs imported from a digital camera or a smartphone. You can import your digital photos in the software and select the ones that need to be fixed.

In the case of Picasa, choose Tools -> Adjust Date & Time and select a new date for your photos. This will change the “Date Picture Taken” field in the EXIF data of you picturs. Similarly, iPhoto users can choose Photos -> Adjust Date & Time to set the selected photos to a particular date and time.

I however prefer a little-known command line utilitly called ExifTool for such operations since it is much more versatile. To get started, download the ExifTool executable and extract the zip file to your desktop. Now rename the exiftool(-k).exe utility to exiftool.exe and we are all set to adjust the date and time of our photographs.

Unlike the iPhoto or Picasa software that simply set the date and time of a photograph to another time stamp, Exif Tool can “shift” the data and time values associated with a picture. For instance, if your camera’s time was off by 2 hours 30 minutes at the time of capture, you can use ExifTool to shift the time stamp of all your pictures only by that “off” duration.

The sytax is:

exiftool.exe “-DateTimeOriginal+=Y:M:D h:m:s” filename.jpg

For instance, if wish to shift the time of photographs by 5 hours and 30 minutes, the command would be:

exiftool.exe “-DateTimeOriginal+=0:0:0 5:30:0” filename.jpg

And if you wish to perform a negative shift by 1 day, the command would be:

exiftool.exe “-DateTimeOriginal-=0:1:0 0:0:0” filename.jpg

Please refer to this document for the exact syntax and other examples.

While other programs only modify the “Date Picture Taken” (DateTimeOriginal),, Exif Tool can also be used to modify other meta data include the “Date Modified” (ModifyDate) and “Date Created” (CreateDate) fields. The command would be:

exiftool.exe “-AllDates+=Y:M:D h:m:s” filename.jpg

Exif Tool makes a copy of your original photograph before updating the time stamp. The tool is free and available for Windows, Mac and Linux.