Get taken datetime from images.

script.ps1

Add-Type -AssemblyName 'System.Drawing'

function Get-ExifDate ([String]$File) {
    try {
        $bitmap = New-Object System.Drawing.Bitmap -ArgumentList $File
        $binary = $bitmap.GetPropertyItem(0x9003).Value
        $string = [System.Text.Encoding]::ASCII.GetString($binary, 0, $binary.Length - 1)
        return [DateTime]::ParseExact($string, 'yyyy:MM:dd HH:mm:ss', $null)
    }
    catch {
        return $null
    }
    finally {
        if ($bitmap) {
            $bitmap.Dispose()
        }
    }
}

function Rename-ByExifDate ([String]$Directory) {
    Get-ChildItem $Directory -Recurse -File | ForEach-Object {
        $date = Get-ExifDate $_.FullName
        if (-not $date) {
            Write-Host $_.FullName '-- ignored (no information)'
            return
        }

        $name = Get-Date $date -Format 'yyyy-MM-dd_HH.mm.ss'
        if ($name -eq $_.BaseName) {
            Write-Host $_.FullName '-- ignored (already is)'
            return
        }

        $ext = $_.Extension.ToLower()
        Write-Host $_.FullName ---> $name$ext -ForegroundColor Cyan
        Rename-Item $_.FullName -NewName "$name$ext"
    }
}