This guide is a excellent material to get started. My environment is not the same, but with few modifications, i got Sametime and Connections working together.
On the page 208 the author show hot to display connections photos ins Sametime web client instant messages.
If you have a few users it is easy to fill the PhotoURL field but if you have a lot of users you need the power of Domino Agents and @Functions.
This single line agent do the job (I schedule this agent to run once a day)
FIELD PhotoURL :="https://