Display vs Visibility: Avoid bg-image load delays for mobile users.

display.css

/* 
 * image loads on hover.
 * users (think mobile) may experience a delay loading the image.
*/

.class {
  background-image: url('some-image');
  display: none;
}
.class:hover { display: block; }

visibility.css

/*
 * image loads on page-load.
 * no delay on :hover.
*/
.class {
  background-image: url('some-image');
  visibility: hidden;
}
.class:hover { visibility: visible; }