Follow the instructions
1. Generate a GUID and append it as a QueryString in the URL that you will email.
string guid = Guid.NewGuid();
2. Create a mapping table for userId and GUID.
3. When the user clicks on the link Tell a friend, add this GUID to the mapping table against the current user ID.
4. When the user's friend clicks on the link from email, fetch the GUID from the query string and match it against the mapping table. If it contains the GUID received then get that respective user details and show the email receiver with the images of the actual user.