Horizontal lines are known to do that but I think the photos aren't equivalent either way. If you cover the dress up or shoulders down, the middle one has a bigger gap between her legs and wider face without being able to see the stripes from what I see.

Horizontal stripes actually look great on a skinny person. Or any person, if the pattern is good by itself — while these black/white stripes aren't really a shining example of that (though they would work on a twig-shaped heroine in a 60s French new-wave film).

Vertical stripes are typically boring imo.

Flannel's plaid disrupts any curves so it's pretty good for covering up bellies in particular. A big reason I'm a fan of the season of flannel (plus scarfs are nice, too).

The horizontal stripes look the best...