Glossary

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Caption(also: Image Caption, Figure Caption)

In the context of image accessibility, a caption is text that describes or provides context for an image. Unlike alt text, which is typically hidden and read only by screen readers, captions are often visible to all users and may appear below or alongside an image. Captions can…

Caption Crawler(also: Reverse Image Search Alt Text)

A technique and tool that retrieves existing alternative text for web images by performing reverse image searches to find the same image on other websites where it has already been described. Rather than generating new descriptions, Caption Crawler reuses human-written alt text…

Controlled Language(also: CL, Controlled Natural Language)

A restricted subset of a natural language that limits vocabulary, grammar, and style to reduce ambiguity and improve clarity and consistency in writing. In accessibility, controlled language rules can be applied to verify and improve the quality of text alternatives for images,…

DALL-E(also: DALL-E 2, DALL-E 3, DALLE)

A family of text-to-image generative AI models developed by OpenAI that produces images from natural-language prompts. DALL-E models are widely used by content creators, including people with disabilities, to generate visuals without photography or illustration skills, but they…

Diagram Accessibility(also: Accessible Diagrams, Scientific Diagram Accessibility)

The practice of making visual diagrams — including scientific figures, flowcharts, organizational charts, and technical schematics — accessible to people with visual impairments, learning disabilities, or other conditions that affect visual processing. Diagram accessibility goes…

ESP Game(also: Extra Sensory Perception Game)

A human computation game, created by Luis von Ahn, in which two randomly paired online players are shown the same image and independently type words to describe it, earning points when their labels match. The ESP Game was designed to generate accurate, human-validated labels for…

Exif(also: Exchangeable Image File Format, EXIF)

A standard metadata format embedded within image files (JPEG, TIFF, and others) that stores information about how an image was created, including camera model, date, GPS coordinates, and orientation. Exif data travels with the image file through most sharing and editing…

Formal Analysis(also: Formal Analysis (Art))

An art-historical method that examines an artwork's observable formal attributes — composition, color, line, light, texture, scale, space, and style — and how they are organized, independent of biographical or historical context. In accessibility contexts, formal analysis…

Image Processing(also: Digital Image Processing)

The use of computational algorithms to analyze, enhance, transform, or extract information from digital images. In accessibility, image processing techniques are applied to convert visual content into accessible formats for blind and visually impaired users, including generating…

Image Segmentation(also: Region Segmentation)

A computer vision technique that partitions a digital image into multiple distinct regions or segments based on shared characteristics such as color, intensity, or texture. In accessibility applications, image segmentation is used to simplify complex images for tactile…

Information Graphics(also: Infographics, Data Graphics, Statistical Graphics)

Visual representations of data, information, or knowledge designed to present complex information quickly and clearly. Common types include bar charts, line graphs, pie charts, scatter plots, and more complex visualizations. Information graphics pose significant accessibility…

Interpretive Alt Text

Alt text that goes beyond objective, functional description to convey interpretive dimensions of an image such as mood, symbolism, narrative, and aesthetic effect. It is most relevant for images where meaning is carried by formal attributes (composition, color, lighting,…

Longdesc(also: Long Description, longdesc Attribute)

An HTML attribute historically used to provide extended descriptions for images that require more detail than can fit in an alt attribute. The longdesc attribute contained a URL pointing to a separate page or anchor with the full description. While part of HTML 4.01 and…

Natural Language Generation(also: NLG, Text Generation)

A subfield of artificial intelligence and computational linguistics focused on automatically producing human-readable text from structured data or other non-linguistic representations. In accessibility, natural language generation is used to create textual descriptions of visual…

Scalable Vector Graphics(also: SVG)

An XML-based vector image format for two-dimensional graphics that supports interactivity and animation. Unlike bitmap formats (JPEG, PNG, GIF) which store images as grids of pixels, SVG describes shapes, paths, and text mathematically, allowing images to scale without loss of…

Tactile Imaging(also: Tactile Image, Tactile Image Conversion, Visual-to-Tactile Conversion)

The process of converting visual images into tactile representations that can be perceived through touch, enabling blind and visually impaired users to access graphical information. Tactile imaging involves simplifying complex visual content into raised patterns, textures, or…

Text Alternative(also: Alt Text, Alternative Text, Text Equivalent)

A textual replacement for non-text content, primarily images, that conveys the same purpose or information as the visual element. Text alternatives are essential for users who cannot perceive images, including people who are blind or have low vision and rely on screen readers.…

Web Mediation(also: Web Content Mediation, Web Accessibility Mediation)

The process of automatically modifying web content as it passes between a web server and a user's browser, typically through a proxy server or browser extension, to improve its accessibility or usability. Web mediation can add missing accessibility features (such as generating…

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