Trulia just let's you have one photo, so either the feed from your office, franchise or other site that feeds to
Trulia will provide it, or you can submit your listings yourself. Here's the link: http://www.trulia.com/submit_listings/enter. You'll have the opportunity to add a photo during the submission process. You can also then link to your website or someplace else where prospective buyers can see more photos about the properties you have for sale.