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Alt tech appendix

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Appendix for Alternate Text Techniques Document


Appendix A: Emerging Technology & Future Solutions

Embedded Metadata

Embedded metadata in images is an example of a simple fix to the "aggregator problem" -- how to provide human parseable metadata while bulk-uploading images. Another advantage of embedded metadata is that it makes possible a "central depository" which can be used to compare and/or overwrite the embedded metadata -- a mechanism akin to the database search one routinely performs for an audio CD; where multiple results are returned, one simply reviews each result, and picks that which best fills/meets one's needs at that particular time.

Embedding Metadata

RDFPic [RDFPic] is a tool developed by the W3C to embed an RDF description of a picture into the picture itself, as described by Describing and Retrieving Photos using RDF and HTTP [PHOTO-RDF], a W3C Note describing a project for describing and retrieving digitized photos with metadata. It describes the RDF schemas, a data-entry program for quickly entering metadata for large numbers of photos, a way to serve the photos and the metadata over HTTP, and some suggestions for search methods to retrieve photos based on their descriptions. The RDF schema uses the Dublin Core schema as well as additional schemas for technical data. This is a tool which a user could use to add a terse and long descriptor to each image being bulk-uploaded.

Metadata Use Cases

Scenarios for exposing Exchangeable Image File (EXIF), International Press Telecommunications Council (IPTC), and Extensible Metadata Platform (XMP) image descriptions so that users can access include:

  • A photographer takes a photo with his SLR digital camera. He describes the image in camera via text input (LCD monitor and multi-selector). It is stored in EXIF. He uploads that image to a photo image gallery application that does not offer a means to enter a text alternative. He would like to have that text description available for his visually impaired friends to access directly.
  • A graphic designer creates an image in Photoshop. From the file menu, he chooses "File Info" then enters a IPTC headline and description. He uploads that image to a web page. A visually impaired person wants to directly access that headline and description.


  • A way to directly access EXIF, IPTC, XMP data

Possible Solutions


Crowd-sourcing is not yet a reliable solution to providing missing terse and long descriptors. For crowd-sourcing to provide viable terse or long descriptors, there needs to be a storage-and-retrieval system such as those which one can use to get metadata about an audio CD when loaded into a computer or wireless-enabled device. If you, as creator of that image, properly annotate it, then your metadata should be presented to the user as the default metadata, and then the user should be able to choose amongst other terser or longer descriptions.

Matt May envisioned an attribute to facilitate crowdsourcing. He said,

I don't want to propose a solution to the problem when I think the status quo in HTML 4.01 doesn't need to be mucked with. But, okay, you read a big long accessibility article, so here's a thought experiment. Add an attribute. Call it @usergenerated. When a UA encounters this attrib, it indicates that the author has stated alt cannot be provided programmatically. It would be even better if other users could detect that attrib and annotate the attached image. If you could get around the spam potential, this could be a real winner. Crowd-sourced @alt. That’s actual accessibility progress, measurable today. If you can't do that much, leave @alt alone.

It would probably require a hash of images with @usergenerated or @missing and the obtain value(s) submitted for them. We would need a canonical URI (or in HTML5, an 'origin') for the document and an ID for the image, but if we had a service (either local or remote) that accepted the URI and its @alt value, then users of AT could associate the values as needed. The worst case is that nothing is returned. (The second-worst case is that it's a bogus value, but the owner of the document could manage submitted @alt content.) The pointer to where to send this information could be in a <link> element, and it could be a standard HTTP request, or a transaction using the HTML5 Database object. It could be hosted locally, or by a third party.

If/when crowdsourcing becomes viable, it would get around one of the biggest problems with images: that we can see something is wrong with someone else's content, but can't do anything about it. With this method people who know what they're doing could directly impact the accessibility of another organization's content. This is in the spirit of initiatives such as Webvisum, Fix the Web, and the Social Accessibility Project, a utility that enables volunteers to make Web pages accessible to the visually impaired. It might help image gallery sites since the image creator or anyone who views the image could propose usable text alternatives with an extremely low-bandwidth solution.

The option to choose among metadata options is necessary, as there are cultural considerations that need to be taken into account. It remains an open question whether there are significant cultural differences in perceptions of a common image. Given such cultural considerations, if a user came from from country X and spoke language Y, that user might want to at least check and compare the metadata submitted from country X in language Y to ascertain that which would be self-evident to a sighted user from country x in language Y.


Crowdsourcing References

Meta Data References

Related References