CSS image replacement

CSS image replacement is a Web design technique that uses Cascading Style Sheets to replace text on a Web page with an image containing that text. It is intended to keep the page accessible to users of screen readers, text-only web browsers, or other browsers where support for images or style sheets is either disabled or nonexistent, while allowing the image to differ between styles. Also named Fahrner image replacement for Todd Fahrner, one of the persons originally credited with the idea of image replacement in 2003.

With the introduction of CSS web font support in all major web browsers, CSS image replacement is now little used.

Motivation
The typical method of inserting an image in an HTML document is via the  tag. This method has its drawbacks with regards to accessibility and flexibility, however:


 * While the  attribute is designed for providing a textual representation of the image content, this precludes the use of HTML markup in the textual representation and causes problems with some search robots.
 * Using the  tag to show text is presentational; many Web designers argue that presentational elements should be separated from HTML content by placing the former in a CSS style sheet.
 * Images referenced using an  tag cannot be easily changed via CSS, causing problems with alternative stylesheets.

Fahrner image replacement was devised to rectify these issues.

Implementations
The original Image Replacement implementation described by Douglas Bowman used a heading, inside of which was a  element containing the text of the heading:

Through style sheets, the heading was then given a background containing the desired image, and the  hidden by setting its   CSS property to  :

It was soon discovered, however, that this method caused some screen readers to skip over the heading entirely, as they would not read any text that had a  property of. The later Phark method, developed by Mike Rundle in 2003, instead used the  property to push the text out of the image's area, addressing this issue:

The Phark method had its own problems, however; in visual browsers where CSS was on but images off, nothing would display.

Also in 2003, Dave Shea's eponymous Shea method solves both of the issues earlier mentioned, at the cost of an extra :

By absolutely positioning an empty  over the text element, the text is effectively hidden. If the image fails to load, the text behind it is still displayed. For this reason, images with transparency cannot be used with the Shea method.

Over a dozen different methods has since been developed with varying degree of compatibility and complexity.