This works to count *.jpg files.
PS C:\\> @([System.IO.Directory]::EnumerateFiles(\'C:\\Users\\Public\\Pictures\', \'*.jpg\', \'AllDirectories\')).Count 8
I don't think you can. Unless you want to implement directory traversal yourself you're probably stuck with something like this:
Get-ChildItem 'C:\Users' -Filter '*.jpg' -Recurse -Force -ErrorAction SilentlyContinue