Preserve the native source
Keep the original file and its acquisition context. Use a copy for cropping, enhancement or format conversion. Record each transformation and preserve the unmodified version. Messaging uploads, screenshots and re-encoding can remove metadata, signed credentials or compression signals needed by a method. A file hash supports identity tracking; it does not establish authenticity.
Choose the format that retains the signal
- JPEG compression and splicing diagnostics require JPEG-specific information; a never-JPEG image cannot supply it.
- Lossless hidden-data screening uses suitable PNG, BMP or TIFF input rather than recompressed JPEG.
- The described document metadata workflow reads JPEG, TIFF or PDF; it does not read PNG metadata.
- Document signature cropping accepts image pages. Confirm PDF support for the particular extraction workflow rather than assuming every module reads PDF.
Consult the selected inventory entry before conversion. Converting an unsupported file into a permitted extension does not create the missing underlying signal.
Check specialist capture requirements
- Writing-speed and pressure measurements need genuine digitizer captures with real timing, pressure and pen-state data.
- Indented-writing enhancement requires raking or oblique light.
- Watermark enhancement requires a transmitted-light photograph.
- Printer identification needs an eligible colour-laser identification pattern and suitable scanning resolution.
- Mains-hum continuity analysis needs a detectable hum trace; absence of a trace is not proof of tampering.
Prepare independent references
Record where known signatures, handwriting, recordings or camera frames came from. Keep natural variation rather than choosing only superficially similar examples. Do not treat duplicated crops as independent samples. A camera sensor comparison needs at least eight suitable native-resolution, well-exposed reference frames; one reference is not an adequate substitute.
Record assessability and missing information
Note blur, clipping, compression, occlusion, weak contrast, short duration and uncertainty about provenance. Explain gaps in the reference set. If a method cannot assess the material, report that limitation rather than forcing a binary result.
Before transferring case material
Agree authority, examination scope, processing arrangements and retention through an approved channel. This website’s enquiry form takes general questions only. Keep evidence attachments and confidential identifiers out of the form.