The 2-Senses Principle

Images and text alternatives

Images, be they illustrations, photographs, graphics, symbols or icons, also convey important information. In all cases, it must be explicitly stated as text (in HTML usually as an alternative text attribute: alt="conveyed info") what information the respective images convey for sighted people.

Images must be described in alternative texts. There are four categories:

• Simple image: The alternative text concisely describes the relevant information of the image.
• Linked image: The alternative text describes the link target.
• Decorative image: The alternative text attribute is empty (alt="", in html) so that the image is ignored by assistive technologies.
• Complex images: These contain a lot of information and must be described in detail outside the alt-attribute, e.g. in the body text or in an appendix. The alternative text itself refers to the detailed description.

> Further information on the accessibility of images and alternative texts

In the context of teaching, special attention must be paid to complex scientific representations that not only depict individual elements but also represent complex interactions between them.

Audio and Video

It is therefore extremely important that any purely visual or auditory information is always explicitly prepared for at least one other sensory quality.

Text is considered a "wild card" and can be automatically prepared for different sensory qualities using modern assistive technologies: Auditory and tactile by means of screen readers or can be read directly visually as text.

> Further info on accessible videos

• The auditory content of videos must always be offered as text in the form of synchronous subtitles.

• The visual content of videos must always be conveyed auditorily as well. Either as integrated description as part of the 'normal' audio track or as an additional audio track, as an audio description.

• The information conveyed in audio files must also be offered in the form of a text transcript.