Just a minor suggestion: what's the point in showing arrows on the lightbox to flip between images if there's only one? If it's possible, I think the arrows (and maybe the "1/1" text) could be removed if the lightbox is only showing one image.
I dunno if it's been mentioned but wouldn't it be better have the larger navigation arrows stacked on top of one another rather than on the left and right hand side of the lightbox saving time in scrolling across the page to check a previous image.