Oh nice, the best takeaway from this (for me) was that desandro apparently has created a hack to deal with the whole is-an-image-in-cache-or-isn't-it problem:
Another thing to be careful with are social buttons, whose height may change after the initial item is rendered. That's easily avoided with a fixed CSS height, though.
However, if you're only in control of the front-end and are just reading from an API of photos where you're given a stream of image urls...how do you determine which css-selector (i.e. '.vert-image' and 'horz-image' with defined h/w dimensions) to put out? You can obviously just restrict everything to a one-size box, but either the vertical or the horizontal images are going to be given short shrift.