If you zoom in and look at the far end of the platform, you'll see the security guard talking to another photographer, who happened to come on the same train I did. That security guard later came for me and told me to leave for 'loitering'. Totally ridiculous and pointless.
UPDATE 12/24/09: I sent a complaint to Sound Transit on the same day. I got a reply the next day.The PR folks there actually know me well. They talked to the security department and suggested that I print a "press pass" to avoid that issue.