Security and Privacy in OCR

Advanced Guide: Security, Privacy, and Client-Side Trust

This section details practical safeguards that complement the client-side architecture. It focuses on secure data handling in the browser, supply-chain hygiene for dependencies, and user-visible assurances that keep sensitive documents safe—all without changing the page’s UI or existing workflows.

1) Threat Model & Data Lifecycle

Treat every input as sensitive. The lifecycle is simple: load → decode → recognize → display → optional export → tab close. Data lives in memory only. Avoid writing recognized text to persistent storage unless a user explicitly downloads it. When results are copied to the clipboard, it happens through a deliberate user gesture.

• Scope: No server upload, no telemetry, no background sync.
• Exposure surface: The browser tab, imported scripts, and any user-triggered exports.
• Goal: Keep content isolated to the tab and ephemeral by default.

2) In-Browser Isolation Basics

• Same-origin discipline: Use only trusted origins for scripts. Avoid dynamic innerHTML with untrusted strings.
• Blob URLs: When previewing images, use URL.createObjectURL() with revocation after use to limit lifetime.
• File type handling: Treat unusual containers conservatively. If you ever display SVGs, render them to canvas rather than injecting raw markup.

3) Content Security Policy (CSP) — Recommended

CSP narrows what the page can load/execute. A minimal, strict policy (set at the web server) might resemble:

Content-Security-Policy:
  default-src 'self';
  script-src 'self' 'wasm-unsafe-eval';
  img-src 'self' blob: data:;
  style-src 'self' 'unsafe-inline';
  connect-src 'self';
  worker-src 'self' blob:;
  frame-ancestors 'none';
  base-uri 'self';
  form-action 'self';
  

This keeps execution local, allows WebAssembly/Workers for OCR, and blocks unexpected network calls or framing. (CSP is declarative—no code edits on this page are required.)

4) Permissions Policy (formerly Feature-Policy)

Use server headers to disable unneeded sensors/APIs:

Permissions-Policy:
  camera=(), microphone=(), geolocation=(), usb=(),
  screen-wake-lock=(), serial=(), payment=()
  

5) Cross-Origin Isolation for Performance & Safety

When high-performance WASM paths need SharedArrayBuffer, enable cross-origin isolation with:

• Cross-Origin-Opener-Policy: same-origin
• Cross-Origin-Embedder-Policy: require-corp

This grants modern performance primitives while preventing cross-origin interference.

6) Dependency Hygiene & Supply-Chain Safety

• Version pinning: Use specific versions for core libraries to keep behavior reproducible.
• Subresource Integrity (SRI): Attach integrity hashes to external scripts to detect tampering.
• Fallback strategy: Prefer loading from your own origin; if a CDN is used, verify hashes at build time.
• Minimal surface: Keep the dependency list short to reduce attack surface and update burden.

7) Local-Only Exports & Download Hygiene

• Exports are generated in memory and offered via a user-initiated download.
• Use file names that avoid leaking content (no automatic inclusion of document titles).
• For structured exports, include only necessary metadata (page and region ids) and omit any accidental PII.

8) Clipboard, Cache, and Storage Considerations

• Clipboard: Only write on explicit clicks; do not poll/read clipboard without a visible action.
• Cache: Avoid caching user documents in Service Workers by default; keep model/data assets cached, but not content.
• Storage: Refrain from storing recognized text in localStorage/indexedDB unless a user opts in.

9) Handling Sensitive Documents

• Encourage users to review outputs before sharing—especially IDs, medical notes, or financial numbers.
• Strip EXIF metadata when re-encoding previews; it can contain capture location and device details.
• Keep a visible “clear” action that discards in-memory data from the UI.

10) Error Messages Without Data Leakage

Show concise, actionable errors (“image too large,” “rotate to portrait”) without echoing user content. Avoid embedding any snippet of recognized text into console logs or error analytics.

11) Privacy by Design — Practical Habits

• Default to the least data necessary; do not infer or classify beyond OCR’s purpose.
• Keep settings ephemeral per tab; require user action for persistent preferences.
• Document the “no upload” guarantee in plain language directly near upload controls.

12) Regulatory Alignment (Informational)

While this page is not legal advice, client-side processing maps well to data-minimization principles in common privacy frameworks. Users remain controllers of their data; the tool processes locally and does not retain or transmit content by default. If organizational policies require records, make retention strictly opt-in and transparent.

13) Security Testing & Transparency

• Smoke-test with intentionally malformed files (huge dimensions, odd color profiles) to check robustness.
• Practice “explainability”: publish a short note about local processing and what the page does not do.
• Provide a simple channel for users to report suspicious behavior or vulnerabilities.

14) Incident Playbook (Client-Side Context)

1. Identify: Describe the symptom (unexpected network calls, script errors, UI anomalies).
2. Contain: Instruct users to hard-refresh; operators temporarily roll back the last dependency bump.
3. Eradicate: Remove or pin the offending resource; verify with SRI.
4. Recover: Re-publish with a signed/hashed build; add a brief post-mortem to the site’s changelog.
5. Learn: Add or tighten CSP directives that would have blocked the issue.

15) Accessibility & Safety Together

Security shouldn’t block usability. Keyboard and screen-reader users can complete every action without exposing data beyond the tab. Progress and error messages belong to ARIA live regions rather than pop-ups that could be captured by overlays.

16) Case Study: Confidential Invoices

A small team processed sensitive invoices on shared laptops. By keeping processing local, disabling SW caching of user content, and pinning OCR dependencies, they retained control of data while improving trust. A simple checklist (“clear after export, review totals, avoid re-encoding JPEGs”) removed most residual risk without any UI change.

17) Quick Security Checklist

• All recognition runs locally; no background network calls.
• Exports are user-initiated and ephemeral; filenames do not reveal content.
• No persistent storage of recognized text unless a user opts in.
• Strong CSP + Permissions-Policy set at the server; dependencies pinned with SRI.
• Service Worker does not cache user documents by default.
• Provide a visible “Clear” action and explain local-only processing near the upload control.

Summary

Client-side OCR is inherently private when paired with disciplined dependency management and restrictive headers. Keep data in memory, make exports explicit, and confine execution to trusted resources. These practices turn “no upload” from a promise into a verifiable behavior users can rely on.