You're not just that woman in the photo who calls the office every couple of days, so show her a bit of presence: never miss a work dinner, meet him for lunch or for dinner at the office and circulate a bit, oozing friendliness and intelligence (not like Bridget).
Be careful not to show the slightest sign you're jealous of her and don't ever criticise her - he'll resent it, it could push them closer together and make him see her differently, even if he'd never noticed her endless legs and model figure up until now...
You could also try making him jealous to keep him on his toes and make him prove to you that he loves you. You could always slip something in about your new work colleague you get on really well with, who just so happens to be charming, handsome, five years younger and moonlights as a model. However, be careful he doesn't call your bluff by raving about his gorgeous, talented workmate - it could blow up in your face!