To add picture for mail sender:

1. Open Exchange Management Console.

2. Run this command:

Import-RecipientDataProperty -Identity <id> -Picture -FileData ([Byte[]]$(Get-Content -path "C:\Users\Administrator\Pictures\<id>.jpg" -Encoding Byte -ReadCount 0))

Result:

User photo will appear in global address book like this:

Source picture: http://www.msexchange.org/articles_tutorials/exchange-server-2010/management-administration/configuring-using-display-picture-exchange-server-2010.html