Site Photography and Illustration

The four elements that forensic site photography demands can be remembered as SNCR: scale, north arrow, colour checker, RAW. Each has a specific evidential function. Together they make the photograph interpretable, measurable, colour-calibrated, and preserving of original data. The absence of any one element is a technical deficiency that an opposing expert or a judge can note.

• Scale bar: placed in the plane of the feature being photographed (not on one side where the lens perspective will distort its apparent length relative to the subject). For plan-view photographs of a grave floor, a 1 m scale bar across the short axis is standard.
• North arrow: a physical north arrow card (magnetic or true north, stated) placed in frame for every plan-view photograph. For vertical section or detail photographs a north arrow may not be applicable, but view direction should be noted in the photographic log instead.
• Colour checker: photographed once at each lighting change (shift in cloud cover, move to artificial light, change in camera settings). The colour-checker image allows post-processing to calibrate the RGB values of soil, bone, and fill to a known reference, so that colour comparisons between photographs are valid.
• RAW format: set on the camera before the first photograph is taken. If the camera does not support RAW, the limitation should be noted in the photographic log and the camera's JPEG compression level should be set to the highest quality available.

A systematic photography protocol distinguishes three levels of shot, each with a defined purpose in the site record. All three levels are taken at each significant stage of the excavation, not just at the end.

A common error is to take only the context-level shot and omit the detail shots for small finds or bone trauma. Once the element is lifted and bagged, a photograph showing its in-situ relationship to adjacent material is gone. The protocol should specify that every registered find receives both a context-level shot (showing its position in the context) and a detail shot (showing its surface characteristics).

Every photograph taken at a forensic site generates two records: the digital image file and a photographic log entry. The log entry is the link between the image and the context recording system. Without it, a court looking at a photograph cannot be sure when it was taken, by whom, what context it represents, or whether it is the original unaltered file. The log is kept on paper during fieldwork and incorporated into the digital site archive during post-excavation processing.

Chain of custody for digital images follows the same logic as chain of custody for physical exhibits. The camera card is treated as primary evidence. Images are copied (not moved) from the card to a designated evidence drive immediately after each session. The card is retained or written-protected. A hash value, typically SHA-256, is generated for each image file at the point of ingestion. The hash is recorded in a transfer log alongside the file name, date, time, and operator. Any future copy of the file can be re-hashed and compared to the original hash to confirm the file has not been altered.

A context plan is a hand-drawn record of the horizontal extent and surface features of one context, made at 1:10 or 1:20 on film drawing film or waterproof paper, with a fixed north arrow and the context number, site code, date, scale bar, and drafter's initials on the sheet. It documents the shape, extent, and visible characteristics of the context surface at the precise moment of recording, before any further excavation changes it.

• 1:10 scale: used for contexts where centimetre-level detail is needed: individual skeletal elements, finds clusters, small features. A 2 m grave would be drawn on a 200 mm wide sheet at this scale.
• 1:20 scale: used for context outlines and larger features where overall shape and relationship to adjacent contexts is the primary information. A 4 m grave cut fits on a standard A3 sheet at this scale.
• Offsetting: the outline of the context is plotted by measuring perpendicular offsets from a tape stretched along the long axis of the feature (the baseline), or by plotting total-station coordinates. Both methods must give the same result; a discrepancy indicates a recording error.
• Conventions: cut edges are drawn as solid lines; layer boundaries as dashed lines; finds as circles with an F number; skeletal elements with their anatomical abbreviation. Standard conventions from the Museum of London Archaeology (MOLA) recording manual are widely adopted as forensic practice.

A section drawing documents the vertical stratigraphic profile exposed when an excavated trench or grave is cut through and the side walls cleaned back to expose the layers. It is the primary record of the relative age of contexts (which layer cuts or seals which), the depth and angle of fills, and the relationship between the grave and surrounding natural or made ground.

A horizontal datum string is stretched across the top of the section at a known height. The section drawing is referenced to this string: all vertical measurements are taken downward from it. The horizontal extent is measured along the base of the section or by total station. Drawing film is clipped to a drawing board and a grid may be pre-printed at 1:10 to speed plotting. Each context in the section is given its context number, described in the written record, and its boundary is drawn as precisely as cleaning and observation allow.

• Datum string height: set at a convenient height above the highest point of the section, typically 100 to 200 mm. Its elevation is measured by total station and recorded on the drawing.
• Cleaning the section face: the vertical face is scraped with a trowel to expose context boundaries clearly before drawing begins. Photographing before and after cleaning shows that boundaries are real stratigraphic interfaces, not trowel marks.
• Symbols: cut edges are shown as solid lines; gradational boundaries as pecked lines; finds in section as triangles with their F-number. The conventions should match those used in the context plans.
• View direction: stated on the drawing (facing north, facing east, etc.). The same section should not be recorded facing in opposite directions on different sheets without an explanatory note.

Every digital image file produced by a camera contains EXIF metadata embedded in the file: camera make and model, lens focal length, aperture, shutter speed, ISO, date and time, and if a GPS-capable camera was used, coordinates. This metadata is part of the evidential content of the image. Courts increasingly ask for the EXIF data to confirm that the stated date and time of photography are consistent with the file.

Before a forensic operation begins, the camera clock should be synchronised to a time source of known accuracy (a GPS time signal or a reference clock) and the synchronisation noted in the photographic log. If the camera clock later proves to have been wrong, the discrepancy can be applied as a uniform correction to the timestamps, but only if the synchronisation record exists.