Here are a few of the times that I have needed to do this: - Changing the battery on my camera switched to a default date. - I wanted to synchronize the time on my camera to a GPS track so the photos matched the timestamped coordinates. - At a family event where images from different cameras were added together.
You can do edit the timestamp using a GUI and many photo manipulation applications like the GIMP support metadata editing. For example on KDE:
gwenview -> plugins -> images -> metadata -> edit EXIF
The problem is that this gets tiresome after a few images, and anyway the times are correct in relation to each other - I just need to add or subtract a time correction to them en masse.
The answer: exiv2 - Image metadata manipulation tool. It is a program to read and write Exif, IPTC and XMP image metadata and image comments.
user@pc:~$ exiv2 *.jpg File name : test.jpg File size : 323818 Bytes MIME type : image/jpeg Image size : 1280 x 960 Camera make : FUJIFILM Camera model : MX-1200 Image timestamp : 2008:12:07 15:12:59 Image number : Exposure time : 1/64 s Aperture : F4.5 Exposure bias : 0 EV Flash : Fired Flash bias : Focal length : 5.8 mm Subject distance: ISO speed : 160 Exposure mode : Auto Metering mode : Multi-segment Macro mode : Image quality : Exif Resolution : 1280 x 960 White balance : Thumbnail : image/jpeg, 5950 Bytes Copyright : Exif comment :
The trick is to pick a image where you can that figure out what the time was and work out the time offset. In my case I needed to adjust the date forward by six months and four days while changing the time back by seven hours. I used the command
exiv2 -O 6 -D 4 -a -7 *.jpg
-a time Time adjustment in the format [-]HH[:MM[:SS]]. This option is only used with the 'adjust' action. Examples: 1 adds one hour, 1:01 adds one hour and one minute, -0:00:30 subtracts 30 seconds. -Y yrs Time adjustment by a positive or negative number of years, for the 'adjust' action. -O mon Time adjustment by a positive or negative number of months, for the 'adjust' action. -D day Time adjustment by a positive or negative number of days, for the 'adjust' action.
When we run this we can see that the timestamp has now changed.
user@pc:~$ exiv2 *.jpg | grep timestamp Image timestamp : 2009:06:11 08:12:59
That's it. Remember this is the end of the conversation - to give feedback you can either record a show for the HPR network and email it to firstname.lastname@example.org or write it on a post-it note and attach it to the windscreen of Dave Yates's car as he's recording his next show.