Allow user to keep a number of stored photos in their profile. Then allow user to change photos on the fly - even in the middle of a Lync conversation session.
Useful example would be to show photo based on what project or responsibilitites you are working on that week/month. On the lighter side, you could click to change the photo MOOD for the day, or even for the current conversation. Example, while discussing something heated, change your photo to one of your concerned expressions. the same functionality would follow for OUTLOOK with even more usefulness. Select a profile photo of yourself to display for that particular email message, which would help convey the mood of the email, display your agreement or opposition, etc.