Before-and-after thumbnail

Two images sit side by side, sometimes with a divider or an arrow, showing what something looked like before and what it looks like after. Renovation, fitness, restoration and makeover channels lean on it because the transformation is the whole promise and a still image can carry it without text. It works when both halves are obviously the same subject and the difference is readable at phone size. It fails when the before has been staged to look worse than it really was, or when both halves are so busy that neither registers in the feed. One clear change beats four small ones.