to active
state 
and
presenting a title.longdesc DiscoverabilityInnovative browser vendors and developers provide ways that make
longdesc discoverable to sighted users. These
include:
Opera's
TellMeMore extension provides an icon in the chrome to indicate
when descriptions exist. The user is notified by the icon changing
from an inactive state to active
state and
presenting a title.
Upon activating the icon, the user is presented with a popup containing a list of all descriptions available along with their thumbnail images.
Then when the user selects a link in the popup, a new tab is opened with a text description in it.
Note: a variation on this method is a Yandex extension, which provides the icon in the address bar rather than the chrome.
Opera and iCab provide context menu functionality natively. Longdesc Firefox Extension provides a context menu. A Chrome plugin by Chris Kennish highlights and provides right-click access to image long descriptions. IE can be configured to add context menu. In addition iCab provides users a visual clue by changing cursors from a standard cursor to a special contextual-menu cursor upon encountering an image with a long description.
A user agent could allow users to navigate browsing contexts to the resource, or replace images with their long text alternatives according to user preference.
If a "Display Image Descriptions" preference is selected by a user, a user agent could then superimpose an icon or button directly on or beside the image itself whenever descriptions are available.
Upon activating the icon or button the image could disclose the description in addition to the image or it could replace the image with the description.
This type of direct replacement functionality is provided in a scripted longdesc implementation. The preference panel image is an adaptation of iCab's preferences panel.
Tools such as FireFox's
Longdesk extension and Jim
Thatcher's universal longdesc favelet make longdesc discoverable to sighted users via on-page links.
FireFox's Longdesk Extension by Anthony Ricaud adds a link to the longdesc under images that have a longdesc attribute. A user agent could allow users who want an image description link on screen this option according to user preference.
A powerful and universal longdesc favelet by James
Thatcher first announces the number of images on the page that
have longdesc attributes.
Then it highlights each image on the page that has a
longdesc and provides on-screen text links to each
corresponding description.
For the functional favelet drag longdesc to your bookmarks. Tested in Chrome, FireFox, Internet Explorer, Safari, Opera, and iCab.
Chris Kennish's longdesc chrome plugin is an example of providing a long description according to user choice while not forcing a visual encumbrance upon them. Once the extension is installed the user is provided with the following customization preferences.
Touch device activation could be upon:
A touch User Interface ( UI ) could utilize a "turn the image around" transition e.g., the UI could have a flip transition akin to flipping over a hard-copy physical photograph to read what is written on the back.