Extracting UserAttribute (photo)

[Sascha Kiefer]

David Shaw wrote
 >
 > photo-viewer "cat > ~/photoid-for-key-%k.%t"

What is the syntax of the photo-viewer parameter?
i tried the following:

gpg.exe --photo-viewer "C:\Path\Of\Viewer\viewer.exe" --edit mustermann 
showphoto quit

and gpg says:
gpg: this platform requires temporary files when calling external programs
gpg: unable to display photo ID!

As you can see i'm running it on a windows system!

Thanks!