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Short answer

Alt text (alternative text) is a short description that conveys what an image means. Screen readers read it aloud when they reach the image, so without it people who use screen readers miss the image's content. It is required under the U.S. federal Section 508 guidelines for digital content. [S1][S2]

Key points

• Describe what the image is meant to convey, not every pixel. [S1]
• Alt text also helps people with slow connections where images do not load. [S1]
• Section508.gov is the federal hub for IT accessibility guidance, including accessible websites and documents. [S2]

Claims

• id: C1 claim: Alt text conveys the meaning of an image in digital content. source: S1 evidence: "descriptive text that conveys the meaning of an image in digital content"
• id: C2 claim: Screen readers read alt text when they reach an image. source: S1 evidence: "When the screen reader reaches an image, it will read the alt text"
• id: C3 claim: Alt text is required by the Section 508 guidelines. source: S1 evidence: "alt text is a requirement in the Section 508 guidelines"
• id: C4 claim: Section508.gov gives federal agencies accessibility guidance on websites and documents. source: S2 evidence: "including creating accessible websites and documents, accessibility testing"

Sources

• [S1] Authoring Meaningful Alternative Text. Section508.gov (GSA). https://www.section508.gov/create/alternative-text/ . License: US government work, public domain. Accessed 2026-11-04.
• [S2] Accessibility. Section508.gov (GSA). https://digital.gov/topics/accessibility . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_2m0cdaed,
  author = {{iinventedlight}},
  title = {{Alt text: what it is and why images need it}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/alt-text-basics/},
  note = {Permanent ID iil:note:2m0cdaed. License: CC-BY-4.0.},
}

Markdown

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