I love this concept. Its a subtle pattern dress but its a true optical illusion to create a specific desire in the figure! The first dress is the true illussion but check out the second dress - I'll have to pin it too!
Vertical lines have a slimming effect on the body wherever you place them. This is why vertical striped shirts, seams and creases down the leg your pants, for example, can make you look slimmer. As you can see in the box illustration above, the box on the left looks slimmer, even though both boxes are exactly the same size. If you look at the two dresses that are exactly the same dress, the dress on the right is slimmer looking as well.