Problem: When you are attempting to open pictures from WebDAV in Microsoft Office Picture Manager, you see the following error message:
Picture Manager is unable to open pictures over the Internet that are not from a Windows SharePoint Services picture library. Please specify a valid picture library and try again.
This message occurs because Microsoft Office Picture Manager does not support the standard WebDAV protocol.
To work around this problem:
Copy the picture file to your local machine, then open the file using whatever photo viewer you want.