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Image Performance Handoff for Outsourced Websites

A practical research guide to image inventory, dimensions, alternatives, licensing, and performance evidence.

Image Performance Handoff for Outsourced Websites editorial illustration

Image work is a content, accessibility, legal, and performance handoff. A useful register connects each asset to its source, license, crop, alternative text, page, dimensions, and optimization decision.

Key Stats

  • Core Web Vitals has 3 metrics (web.dev)
  • WCAG 2.2 has 4 principles (W3C)
  • The HTML image element supports a width and height attribute pair (WHATWG)

    • Key Takeaways

  • Keep source and license notes beside the production asset.
  • Write alternative text for the purpose of the image in context.
  • Measure the page after image changes.

    • Methodology

    Official web, accessibility, and performance specifications define the checks. Recommendations are a workflow for outsourced website production, not a performance guarantee.

    Asset register

    Record filename, source URL, creator, license, permission evidence, crop, intended page, alternative text, intrinsic dimensions, rendered dimensions, format, and reviewer. Flag decorative images separately from informative images.

    Review evidence

    Compare the register with the built page. Check text alternatives, layout stability, responsive behavior, loading behavior, and the page performance report. Keep the before and after route and test conditions.

    Sources

    1. W3C WCAG 2.2 Non-text content requirements.

    2. W3C Images tutorial Image alternative guidance.

    3. WHATWG HTML images Image element specification.

    4. Google Core Web Vitals Performance metrics.

    5. web.dev Learn Images Image delivery guidance.

    6. MDN responsive images Responsive image reference.

    7. Google Search Central image SEO Image search guidance.

    8. Creative Commons licenses License reference.

    9. Schema.org ImageObject Image metadata vocabulary.

    10. Sitemaps protocol Sitemap protocol.

    Further reading

    Image license checklist

    Performance budget handoff

    Related Research

    Core Web Vitals workflow

    Content ownership

    Accessibility test plan

    Frequently asked questions

    Is a filename enough to document an image?

    No. Preserve source, license, context, alternative text, and intended use.

    Should every image receive the same alternative text treatment?

    No. The text depends on whether the image conveys information, acts as a control, or is decorative.

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