Try this, not a completely perfect script but it works as long as you provide the URI with a '/' at the end. Some images are stored on slightly different paths than the URI you may be requesting, so for exmaple here 'google.com/' wasn't working right but making the URI variable 'www.google.com/' fixed the issue.
$path = $null
$filter = $null
$uri = 'www.google.com/'
Write-Host "URI: $uri" -ForegroundColor Green
$filter = $uri | Select-String -AllMatches -Pattern '(\w.+)\/'
$path = $filter.Matches.Groups[1].Value
Write-Host "Server: $path" -ForegroundColor Yellow
$site = Invoke-WebRequest -Uri $uri
$images = $site.Images.src
foreach ($image in $images) {
Write-Host "Files that are being downloaded:" -BackgroundColor Black -ForegroundColor White
Write-Host $image -ForegroundColor DarkYellow
Start-BitsTransfer -Source "http://$path$image" -Destination '.\TEMP\' -TransferType Download
}