Seo images media

seo-images-media (M9)

Accessible, well-described media is read by both ranking systems and AI extractors — alt text is the primary semantic handle for an image. Reference: references/schema-tier1.md (VideoObject row).

Audits

Working from the PageSnapshot (rendered_dom if present, else raw_html):

1. Alt presence: every content <img> has an alt attribute. Distinguish decorative images (alt="" + role="presentation" is correct, not a finding) from missing alt entirely (fail).
2. Alt quality: not empty on a content image; not the filename (IMG_2031.jpg); not duplicated verbatim across distinct images; not keyword-stuffed (comma-separated keyword lists are an anti-pattern). Alt should be descriptive and contextual to surrounding content. Target length ~80-140 chars — long enough to be specific, short enough that screen readers/AI don't truncate.
3. Dimensions: width and height set on <img> (or aspect-ratio reserved in CSS) to prevent layout shift (CLS, a Core Web Vitals input — defer the CWV measurement itself to the perf module).
4. Format: flag legacy jpg/png where a modern format (WebP/AVIF) or a responsive <picture>/srcset would serve smaller bytes.
5. Video: embedded video (<video>, YouTube/Vimeo iframe) without VideoObject JSON-LD — coordinate with M5; required/recommended props in references/schema-tier1.md.

Fixes

• AUTO (fixable: auto): add width/height to <img> from the source asset's intrinsic dimensions (deterministic, additive, verifiable) — emitted as a diff for fix.
• PROPOSED (fixable: proposed): generate contextual alt text inferred from the image plus its surrounding heading/caption/paragraph. Drafts require per-item human accept (alt is editorial). Never fabricate what an image depicts beyond what the page context supports — leave a clearly-marked TODO: describe image placeholder when context is insufficient, or ask the user.
• ADVISORY (fixable: advisory): format upgrades (WebP/AVIF, srcset). The tool cannot transcode binaries, so it never writes these — it recommends only.

Verification

• Method dom_assert: re-parse the snapshot and assert the condition (alt non-empty, width+height present, not a filename, etc.).
• When dimension checks need the intrinsic size of a remote asset and no fetch tier is available, status is needs_api, never a false pass.

Findings

Emit findings per schema/finding.schema.json. Examples (all severity 3, axis both):

• M9.alt.missing — content <img> with no alt attribute. status fail, fixable: proposed, confidence established. evidence.observed quotes the offending <img> tag.
• M9.img.no_dimensions — <img> lacking width/height. status warn, fixable: auto, confidence directional (CLS link).
• M9.video.missing_videoobject — embedded video without VideoObject schema. status warn, fixable: proposed, confidence established. Each finding: evidence.observed quotes the page; verification.reproduce is runnable, e.g. node scripts/parse-html.mjs --url <u> then inspect the images block (missing_alt, empty_alt, missing_dimensions). expected_impact is banded + confidence-tagged (no naked %).

Honesty

• Alt text aids accessibility and image/AI understanding; treat ranking lift as directional, not a guaranteed gain — do not promise traffic from alt rewrites.
• Keyword-stuffing alt is harmful, not helpful — flag it, never generate it.
• WebP/AVIF reduce bytes (a real perf input) but format alone is not a documented ranking factor; keep it advisory/low magnitude.