How do digital forensic labs determine whether files on a device were created locally or copied from another source?
Executive summary
Digital forensic labs combine low-level acquisition, artifact correlation, and content/format analysis to decide whether a file originated on the examined device or was copied there from elsewhere; no single signal is definitive so analysts build a timeline from timestamps, file-system metadata, OS artifacts (shortcuts, link-tracking, backups), and file-internal markers such as EXIF or application fingerprints to reach a best-supported conclusion [1] [2] [3] [4]. These methods are powerful but context-dependent: platform differences, intentional tampering, and gaps in artifact availability mean conclusions are probabilistic and must be reported with caveats [5] [6].
1. The foundation: forensically sound acquisition and hashing
Every credible determination starts with a bit‑for‑bit image or carefully documented logical acquisition so the original media is preserved and verification hashes demonstrate fidelity; labs routinely use write-blockers and produce disk images or logical backups before analysis [1] [7]. Without a reliable acquisition, downstream signals (timestamps, slack space, carved files) cannot be trusted, and examiners must note any deviation from standard procedures [8].
2. File-system metadata: the MAC times and their limits
Analysts first inspect file-system metadata—modified, accessed and created timestamps, inode change times and NTFS MFT records—to see when a file appeared and how it was altered, because a locally created file will typically show creation times aligned with user activity and application logs [9] [10]. However, timestamps can be changed intentionally or by simple copy operations, and different OS behaviors (e.g., preservation or rewriting of creation time on copy vs. move) complicate interpretation, so timestamps are one input among many rather than proof by themselves [5].
3. Operating-system artifacts and provenance traces
Windows LNK (shortcut) files, the Link Tracking Service, and File History or backup records can directly record origin device identifiers, original file paths, and MAC addresses that indicate a file was created or opened on another system, which makes them high‑value provenance signals when present [3] [4]. Mobile and modern OS artifacts (system logs, app caches, SQLite databases) likewise store usage records and backup histories that help tie files to device activity, but availability varies by device model and OS version [6] [11].
4. File-internal fingerprints: headers, metadata and creator tools
Content-level analysis looks inside files for embedded metadata (EXIF in images, PDF producer strings, office-document metadata) and for subtle fingerprints in headers or encoding parameters; JPEG header parameterization and EXIF tags can point to particular camera models or apps, while research into tool identification (e.g., PDF generator fingerprints, ML-based creator identification) can attribute a document to a class of software or device [2] [1]. These signals help distinguish a file freshly created on-device from one copied from a different toolchain, but they can be stripped or altered.
5. Correlation and timeline reconstruction
Best practice is to correlate all signals—filesystem times, OS artifacts, internal metadata, backup logs and network traces—into a timeline showing creation, modification, copy, upload or download events; corroboration across independent artifacts raises confidence while contradictions force cautious reporting [10] [12]. Investigators often parse unallocated space and carved remnants to find older versions or evidence of deletion that indicate a file’s lifecycle prior to its current presence [13].
6. Tooling, vendor biases, and evidentiary explanation
Forensic suites (EnCase, FTK, Cellebrite, Belkasoft and others) automate artifact recovery but require examiners to justify tool choices and understand limitations; vendors may emphasize proprietary capabilities like full file-system extractions or carving features, so analysts must explain methodology and potential biases when presenting provenance opinions [10] [14]. Open‑source techniques and manual inspection remain important counters to overreliance on a single product [13].
7. Limits, adversarial factors and how conclusions are framed
Conclusions about local creation versus copy are probabilistic: metadata can be forged, cloud or backup restores can reintroduce older timestamps, and mobile software diversity means some artifacts simply won’t exist on some devices; therefore labs typically state confidence levels, list relied‑upon artifacts, and present alternative explanations rather than an absolute verdict [5] [6]. When key artifacts are missing or conflicting, responsible reporting must note that the evidence does not definitively resolve origin [4].