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";
}