Having read elsewhere on the site of people's regret at not taking 'before' photos, so I collected together a few recent pics, mostly taken in the 6 weeks before I started this. I plan to take more photos each stone lost. (And yes, they are taken in the ladies at work. Quite odd and perhaps inappropriate, but it's the only place I can get to a full-length mirror and a bit of peace...)
I suppose it depends on how much you've got to lose as to how often you ought to take them, as the lower your start weight, the more of a difference half a stone will make.
But if you want a good reason to take regular photos, take a good look at the slideshow. It'll blow you away...