I went on holiday for two weeks together with my girlfriend. We both had our own camera and when we returned home we wanted to merge both photo collections. There was only a small problem, the date/time settings of the cameras were not in sync. This will give you funny/strange results when viewing the slideshow.

To solve this issue, I created a small powershell script. As an argument you provide a datetime string (format ddMMyyyyHHmmss). The oldest file (inside the directory where you execute this script) will get this new provided creation date. The creation date of the other files is updated taken the same time span (between oldest file date and the provided date) into account. Executing this script on one of the photo collections will make it possible to merge both collections.

$oldestFile = dir | sort-object CreationTime | select -first 1

$newStartDateTime = [datetime]::ParseExact($args,"ddMMyyyyHHmmss",$null)
$timespan = $newStartDateTime - $oldestFile.CreationTime

dir | foreach { $_.CreationTime = ($_.CreationTime + $timespan)}