Overlay an image button (with text) on text, so that when you turn images off it is still accessible.

imageButtonText.css

a.backButton { /* Obviously change the class to whatever you want*/
  display: block;
  width: 50px; /* Width of the image */
  position: relative;
}

a.backButton img {
  position: absolute;
  top: 0;
  left: 0;
}

/*** HTML Markup 

  <a class="backButton href="#">
    Back
    <img src="image.jpg" alt="" />
  </a>

***/