Photographs of a trace should both help locate it on the object and show individual features. This usually requires different images. A single close-up with a ruler may show neither the initial position nor the relationship to the surrounding surface.
Start with an overall view
Photograph the entire object and the position of the area to be examined relative to stable reference points. Then take an intermediate image linking the overall view and the detail. Do not move or clean the object simply for a more striking composition if doing so changes the trace.
How to use a scale
Place a scale reference nearby without covering or touching the significant area. The photographic conditions must make its position relative to the surface clear. The presence of a ruler at an arbitrary distance in the image does not in itself make the photograph suitable for precise measurement.
- Preserve the original files without changing their geometry.
- Photograph available features under clearly documented lighting conditions.
- Record the date, object and location of each image.
- Do not replace the overall view with a set of identical macro photographs.
- Specify all known changes to the surface since discovery.
The trace and its suspected source
If an object is available for proposed comparison, describe and preserve it separately. Do not fit a tool to the trace yourself or make experimental impressions on the surface being examined: this may introduce new features and disturb its original condition.
When a photograph is insufficient
Volume, surface relief, material and faint features may require direct examination. The procedure for removal, packaging and making replicas is agreed with a specialist, taking permissible actions into account. Not every trace can be examined fully from a single image.
What the result explains
The conclusion must show which features are available and which tasks they allow to be addressed. Class similarity in shape is not equivalent to identifying a particular implement. Nor does technical compatibility of an action in itself establish the time or participant in the event.
Before making an enquiry, prepare an inventory of the object, photographs and proposed comparison materials. If the location has already been repaired, state this explicitly. Surviving photographs may be relevant, but their actual content and quality determine the limits of their use.