This MozillaZine article discusses one of the lesser known aspects of the HTML 4 spec - LONGDESC - which allows you to provide an alternative textual representation of an image or embedded object. This is in addition to the standard ALT text and can be longer, preferably describing the contents of the picture. have a look at the article and then try out some of the proposed schemes for indicating that additional information is available to the user. This related article discusses the wider issues of interface design when displaying metadata and alternative representations of content to the user and is well worth reading.