How do I get Linkedin's avatars from an email address

Apps like Xobni show the linkedin avatar from a user when they only have the email address to go bye开发者_StackOverflow中文版. I can't find a way to use linkedin's API to get the avatar by searching on an email address ( https://developer.linkedin.com/documents/profile-api ). Any ideas?

https://developer.linkedin.com/documents/profile-fields see picture-url.