Images and Media Optimisation

Fixtures covering alt-text extraction, image dimension and scaling analysis, encoding-quality and next-gen format opportunities, animated-GIF-versus-video classification, hidden and offscreen image detection, and favicon handling.

Fixtures that let a crawler prove it attributes image-level optimisation signals correctly: which page referenced the image, what the reference markup declared (alt, dimensions, container sizing, loading attributes), and what the image resource itself looked like on the wire.

Families:

• Alt text: a plain <img> with no alt, a srcset reference with alt="", an anchor whose only content is an alt-less image, and correct decorative markup (alt="" with role="presentation") that the empty-alt predicate still flags.
• Dimensions and scaling: an image with no declared width/height and no CSS sizing, and a 1600x1067 image rendered inside a 200px container so a browser discards almost all downloaded pixels.
• Encoding quality: two photo fixtures bracketing the recompression threshold — the larger one also crosses the next-gen format and per-image weight lines, anchoring the whole encoding family.
• Next-gen formats: a photographic-class truecolour PNG, the canonical WebP/AVIF-would-win case.
• Animated content: the same animation as an over-threshold GIF image and as the recommended autoplaying, looping, muted MP4 replacement.
• Hidden and offscreen: eager images that are fully invisible (display:none) or fully below the fold, each followed by a deliberate ~200 ms long task so the defer-offscreen signal is deterministic.
• Favicons: a rel="icon" link to a registered 404, an icon served with a deliberately wrong Content-Type, and a page declaring three sized icon links. No favicon hint exists in the product, so these are capability-only.

Every image body is generated deterministically as PNG bytes with the fixture marker in a tEXt chunk; routes with non-PNG extensions deliberately serve those PNG bytes under the extension’s declared content type. The whole group is safe to crawl; the wrong-content-type icon is moderate because it probes type-mismatch handling.

Fixtures in this category

• Images missing alt text — images-missing-alt-page (safe)
• Linked image missing alt text — images-linked-missing-alt-page (safe)
• Decorative image with empty alt — images-decorative-alt-page (safe)
• Image without declared dimensions — images-missing-dimensions (safe)
• Browser-scaled image — images-scaled (safe)
• Inefficiently encoded image — large saving — images-encoding-q100 (safe)
• Inefficiently encoded image — moderate saving — images-encoding-q92 (safe)
• Photographic truecolour PNG — images-nextgen-png (safe)
• Animated GIF over the video threshold — images-animated-gif (safe)
• Animation delivered as video — images-animated-video (safe)
• Hidden eager image — images-hidden (safe)
• Offscreen eager image — images-offscreen (safe)
• Favicon link to a 404 target — images-favicon-missing (safe)
• Favicon with a mismatched content type — images-favicon-wrong-content-type (safe)
• Multiple sized icon links — images-favicon-multi-size (safe)
• Alt-less image asset — images-missing-alt-asset (safe)
• Linked alt-less image asset — images-linked-missing-alt-asset (safe)
• Decorative image asset — images-decorative-alt-asset (safe)
• Undeclared-dimensions image asset — images-missing-dimensions-asset (safe)
• Scaled 1600x1067 image asset — images-scaled-asset (safe)
• Large-saving photo asset — images-encoding-q100-asset (safe)
• Moderate-saving photo asset — images-encoding-q92-asset (safe)
• Photographic PNG asset — images-nextgen-png-asset (safe)
• Animated GIF asset — images-animated-gif-asset (safe)
• MP4 video asset — images-animated-video-asset (safe)
• Hidden image asset — images-hidden-asset (safe)
• Offscreen image asset — images-offscreen-asset (safe)
• 16x16 favicon asset — images-favicon-16 (safe)
• 32x32 favicon asset — images-favicon-32 (safe)
• 180x180 apple-touch icon asset — images-favicon-180 (safe)
• Wrong-content-type icon — images-favicon-wrong-content-type-icon (moderate)

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