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jpegdate

• Download: jpegdate.exe (96k).

Have you ever forgotten to set the timezone of your digital camera before you went on holiday, and want to fix up the timestamps when you get back? Or maybe you have photos taken on two different cameras, but their clocks were set differently, and you want to reconcile them? This free Windows command-line utility comes to the rescue. It can modify JPEG timestamps, and also rename your images according to their timestamp.

Installation: just save jpegdate.exe somewhere convenient. I save it into my windows directory, so I can run it from the command line.

Adjusting the timestamps of your JPEG pictures

• To bump up the "time picture taken" of a jpeg by 8 hours
  (e.g. because your camera was still in Seattle timezone but you were on holiday in Scotland which is 8 hours ahead),
  open up a command prompt and do

jpegdate "pic.jpg" /hour +8

• To bump up the "time picture taken" of all jpegs in a directory,

for %i in (*.jpg) do jpegdate "%i" /hour +8

• To change the year of all your photos to 2012
  

  for %i in (*.jpg) do jpegdate "%i" /year 2012

• To bump up by 12 years, 8 months and 4 days,
(e.g. because you forgot to set the time when you bought your camera, and this is how much it's out by),

for %i in (*.jpg) do jpegdate "%i" /year +12 /month +8 /day +4

• Technically: you can use any combination of

/year X /month X /day X /hour X /min X /sec X
where X can be a number, or +number or -number for a relative change.
Hour is in the range 0-23, using the 24hr clock.

Renaming files according to their timestamp

• To rename a JPEG file so its name starts with the date it was taken,
  (e.g. because you like to see this information in the filename),

jpegdate "pic.jpg" /rename "%{year}.%{month}.%{day} - %{fn}.jpg"

• To rename all JPEGs in a folder,

for %i in (*.jpg) do jpegdate "%i" /rename "%{year}.%{month}.%{day} - %{fn}.jpg"

• To also include hour/minute that the picture was taken,

  /rename "%{year}.%{month}.%{day} - %{hour}.%{min} - %{fn}.jpg"

• Technically: You can use any string which contains in it any of

%{year} %{month} %{day} %{hour} %{min} %{sec}
%{date} %{time} %{fn} %%

• Technically: hour is always in the 24hr clock, 0-23. The %{date} option is formatted YYYY.MM.DD, and the %{time} option is formated HH.MM.SS. Then %{fn} option includes the filename but not its path or its extension. The double %% displays just a single %.

Setting timestamp according to filename

• If your JPEGs already have filenames of the form "YYYY.MM.DD...." then you can copy this year/month/date into the timestamp:

for %i in (*.jpg) do jpegdate "%i" /datefn

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How it works

The source code is available:

• Download jpegdate-src.zip - source code (C++, for Visual Studio 11)

jpegdate is copyright (c) 2012 Lucian Wischik. You may use the source code and executable in any derivative work, in any way you wish. I'd appreciate a mention but it's not necessary. The source code demonstrates how to read the EXIF headers of a JPEG, and how to memory-map a file into memory.

Jpegdate scans through your JPEG file (which is assumed to be in the EXIF file format, seemingly used by all digital cameras nowdays). It looks for all TIFF / IFD and SubIFD directories. Within each directory, it looks for tags 0x132 (DateTime), 0x9003 (DateTimeOriginal), 0x9004 (DateTimeDigitized)

When reading the timestamp of an existing file, it looks at DateTimeOriginal first; failing that, it looks for DateTimeDigitized or DateTime. The EXIF specification says that these fields are always stored inside JPEG file as strings of the form "YYYY.MM.DD HH:MM:SS", in the 24-hour clock.

When writing to the timestamps of an existing file, it writes to whichever of those three tags are present. It never adds additional tags. Therefore, if your JPEG lacks any timestamp, this program will never add one.

When calculating new timestamps, it works up from Seconds through to Years one at a time. For instance:

• Photo taken at 22:00 on April 17th, "/hour +8", will produce 06:00 on April 18th.
• Photo taken at 22:00 on April 17th, "/hour +8 /day +1", will produce 06:00 on April 19th.
• Photo taken at 22:00 on April 17th, "/hour +8 /day 16", will produce 06:00 on April 16th (because the /day specification overrides)

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