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Evidence media

Evidence is often visual. A scanned filing, photograph, spreadsheet, video still or chart can make a source much easier to inspect. PressChain gives evidence records separate fields for the artifact URI, MIME type, metadata URI and cover URL so applications can render useful previews without losing the canonical source.

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Four different concerns

Treat these fields independently:
  • uri points to the evidence artifact.
  • contentHash commits to the artifact bytes.
  • metadataURI can describe the artifact in richer structured form.
  • coverUrl is a presentation aid.
A thumbnail should never be displayed as if it were the original evidence file.

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MIME-aware rendering

Use mimeType to choose a safe viewer path, but verify the actual response content type too. A sensible application supports a limited allowlist rather than injecting arbitrary returned content into the page. For example:
Unknown types can fall back to a download or external-open action with the URI and hash clearly shown.

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Verify before decorating

If your app fetches the artifact, compute its canonical content hash before showing a verified badge. A successful HTTP response only proves that something exists at the URL. When verification fails, keep the protocol record visible and explain the mismatch.

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Metadata for context

Evidence metadata can include information useful to a reader but inappropriate for contract storage, such as document title, issuer, capture date, page count, archival source, redaction notes or a human-readable explanation. Keep sensitive source information out of public metadata. PressChain provenance is a tool for accountability, not a requirement to expose confidential reporting sources.

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Cover images

For PDFs or datasets, a cover image makes a card understandable at a glance. The cover can be generated by the publishing workflow while the original uri remains the canonical artifact. If the cover disappears later, the app should still render the evidence record from its label, MIME type and provenance fields.

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Cache safely

Evidence viewers often use a CDN or local cache. Cache the artifact by content hash when possible instead of URL alone. That way, a mutable URL cannot silently replace cached bytes under the same identity. A content-addressed cache key also makes it easy to invalidate a bad fetch if the observed hash did not match the protocol commitment.