You can flip images with CSS! Possible scenario: having only one graphic for an “arrow”, but flipping it around to point in different directions.

img {
  -moz-transform: scaleX(-1);
  -o-transform: scaleX(-1);
  -webkit-transform: scaleX(-1);
  transform: scaleX(-1);
  filter: FlipH;
  -ms-filter: "FlipH";
}

Example

Normal

Flipped