How To copy only new files from one folder to another with PowerShell

I'm having a little trouble finishing a powershell script. I have a program that downloads images into a temporary folder, then within an hour it will delete the image files. Occasionally I would like to keep some of the files so I'm creating a powershell script to copy the image files out of the temporary folder to a new folder so that I can sort through them and keep what I want.

This is a one way copy from download folder to a destination folder.
Since the script will be ran every 20 minutes by the windows Task Scheduler, I want the script to compare the files it finds in the download folder to the files in the destination folder to see if it's already there.
If the file is new, then copy it, if it's already in the destination folder, ignore it.
This is purely matching filename only and not doing a binary compare.

Searching the web, I found a script on TomsITpro on "How To Sync Folders With PowerShell". This script copies the files both ways between two folders. As I try to modify this to copy only one way, I'm getting powershell errors.

$DownloadFolder = 'D:\TempImages'
$KeepFolder = 'D:\KeepImages'

$DownloadFiles = Get-ChildItem -Path $DownloadFolder
$KeepFiles = Get-ChildItem -Path $KeepFolder

$FileDiffs = Compare-Object -ReferenceObject $DownloadFiles -DifferenceObject $KeepFiles

$FileDiffs | foreach {
    $copyParams = @{
        'Path' = $_.InputObject.Fullname
    }
    if ($_.SideIndicator -eq '=>')
    {
        $copyParams.Destination = $KeepFolder
    }
    Copy-Item @copyParams
}

This script sort of works and does the compare very well and only copies new files if they already exist. The problem is when I run it from the d:\script folder, it copies all the files to the d:\script folder instead of the destination folder, D:\KeepImages. What am I doing wrong here?

Any help with this powershell script would be appreciated.

Solution

$DownloadFolder = 'D:\TempImages'
$KeepFolder = 'D:\KeepImages'

$DownloadFiles = Get-ChildItem -Path $DownloadFolder

$KeepFiles = Get-ChildItem -Path $KeepFolder

$FileDiffs = Compare-Object -ReferenceObject $DownloadFiles -DifferenceObject $KeepFiles

$FileDiffs | foreach {
$copyParams = @{
    'Path' = $_.InputObject.Fullname
           }
 $Downloadll = $copyParams.path
if ($_.SideIndicator -eq '=>')
    {
      Copy-Item $Downloadll -Destination $KeepFolder 
    }
}

Try this