Jpeg EXIF tag manipulation

# Powershell functions to read and modify the "Date Picture Taken" EXIF tag on jpeg images.

[Reflection.Assembly]::LoadWithPartialName("System.Drawing")

# Define function to return "Date Picture Taken" EXIF Tag value
function get-datetaken {
param ($path)
  $bmp = new-object System.Drawing.Bitmap $path
  $prop = $bmp.GetPropertyItem(36867)
  $date = [System.Text.Encoding]::UTF8.GetString($prop.Value)
  [DateTime]::Parse($date.Substring(0,4)+"/"+$date.Substring(5,2)+"/"+$date.Substring(8))
  $bmp.Dispose()
}

# Define function to set "Date Picture Taken" EXIF Tag value
function set-datetaken {
param ([string]$inputPath, [string]$outputPath, [DateTime]$date)
  $dateBytes = [System.Text.Encoding]::UTF8.GetBytes($date.ToString("yyyy:MM:dd HH:mm:ss")) + 0
  $bmp = new-object System.Drawing.Bitmap $inputPath
  $prop = $bmp.GetPropertyItem(36867)
  $prop.Value = $dateBytes
  $bmp.SetPropertyItem($prop)
  $bmp.Save($outputPath)
  $bmp.Dispose()
}

# Define function to increment "Date Picture Taken" EXIF Tag values by specified TimeSpan
function adjust-datetaken {
param ([string]$inputPattern, [string]$outputDirectory, [TimeSpan]$span)
    gci $inputPattern | foreach { `
        $out = [IO.Path]::Combine($outputDirectory, $_.Name); `
        set-datetaken $_.FullName $out (get-datetaken $_.FullName).Add($span); `
        write-output "$($out): $(get-datetaken $out)" `
    }
}

# get-datetaken "c:\temp\exif\test.jpg"
# set-datetaken "c:\temp\exif\test.jpg" "c:\temp\exif\test-output.jpg" ([DateTime]::Parse("2009/08/05 7:06 PM"))

# $span = [DateTime]::Parse("2010/7/19 10:51AM") - [DateTime]::Parse("2004/12/29 11:37 PM")
# adjust-datetaken "d:\home\photos\2010 Road Trip\DSC*.jpg" "C:\Temp\EXIF" $span