Split-screen thumbnail

Two images set side by side, sometimes with a dividing line or an arrow, sometimes a face reacting on one side to a thing on the other. It works because a comparison is legible at small sizes: the eye gets the structure before it reads a word. The risk is halving your own space. On a phone a thumbnail is about the size of a postage stamp, so two busy photographs each get half of that and neither one reads. Keep one side dominant and cut everything from both halves that is not doing the comparison.