Providing Useful Alternative Text Descriptions and Captioning

Alternative Text Descriptions and Captioning: Basic Requirements for Accessibility

Providing alternative text descriptions for images and captions for audiovisual materials has been a cornerstone of accessibility since the introduction of Section 508 of the Rehabilitation Act of 1973. If you use non-decorative images of any kind in your documents or websites, you should provide an equitable alternative text description. If you use audio or video in your classroom or on your websites, you should provide transcripts or captions for those materials.

Useful Alternative Text Descriptions

Every non-decorative image in a document or on a web page should have an alternative textual description of the content of that image. Decorative images are images that don’t add information to the content of a page. Non-decorative images include graphs, charts, maps, artwork, or mathematical equations. A text description should be provided for each non-decorative image in a document or on a web page. This text description is known as the alternative text description, or “alt text.”

An excellent guide for creating useful alternative text descriptions is DIAGRAM Center’s Guide to Creating Effective Alternative Text Descriptions. This guide contains many examples of alternative text descriptions for scientific diagrams, graphs, maps, artwork, and mathematical equations.

Alternative text descriptions can be added to images, graphs, and charts in Word, PowerPoint, and Excel documents, as well as to images on web pages, via the “alt” attribute of an image. This is a straightforward task in WordPress, Blackboard, and other content management systems. Simply look for an “alternative text” form field when adding an image to a page.


Captioning is the process of converting the audio content of a video, webcast, television broadcast, film, or live event into text and displaying the text on the screen. There are two basic types of captions:

  1. Open captions, which are burned directly onto the source media and cannot be turned off.
  2. Closed captions, which can be turned on or off according to the user need, and are stored in files separate from the source media.

Closed captions are generally preferred to open captions because they can be easily corrected and displayed in many different ways.

If you use audio or video in your classroom or on your websites, you should provide captions for those materials. The university does not provide captioning services directly. It is up to the creator(s) of the audio or video to generate captions.

The following commercial vendors provide high-quality captioning services. Contact JHU purchasing if you seek to use one of these services:

  • 3Play Media (used by the School of Public Health and Engineering for Professionals)
  • CaptionSync (used by the School of Medicine)
  • (used by the School of Education)

Videos posted to YouTube must also be captioned, even though it is a third-party video hosting service.

List of Procurement approved resources for interpreting, transcribing and captioning

Special notes for academic courses:

  • If it is used in your course for recording, Panopto provides a simple checkbox to add captioning. Captioning Panopto recordings is not free and must be paid for through an account with 3Play Media.
  • If you use video content in your course, then it is advisable that videos are captioned to avoid having to pay for the quick turn-around to make them accessible should a student request an accommodation at any point during the course. If you have a student in your class needing accommodation, please direct them to Student Accommodations.