It looks like you're training a short term visual buffer, but I wouldn't assume that generalizes to long term memory.
At times I'll look at something, turn away, but try to hold it in my head, with varying degrees of success. I assume such things can be trained.
But I'd expect their particular method to be relatively ineffective, however, in that it relies on strong contrast in your image, and then strong contrast between that image and the following image. That would train you to better accentuate and perceive that afterimage process, rather than focusing on controlling your visual buffer.
Article can be found here.
I am considering trying this, and I'm wondering if anyone on LW has tried this or something similar. This seems like it could work, but it also seems like it could be hokum. A simple search for "how to develop a photographic memory" returns any number of methods. If this works with the success rate that they imply, this seems like tremendously low hanging fruit.