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Documents can be examined for latent writing impressions and machine generated impressions using the Electrostatic Detection Apparatus (ESDA).
Writing impressions are created in an underlying document by the act of writing on an overlying sheet(s) of paper. Machine generated impressions are (generally) those caused by the transportation mechanisms inside photocopiers, printers, scanners and facsimile machines.
On the resulting ESDA transparency, the developed impressions generally appear black whereas the original ink or printed text on the document being examined generally appear transparent (white on a photocopy) against a grey background.
This technique has been successfully applied in cases involving anonymous letters, dating file notes and diary entries, associating allegedly unrelated documents and associating copy documents with the machines on which they were produced.
It may also be possible to determine whether the writing impressions in a document were generated before or after the original handwriting entries on the same document.
Documents bearing rubber stamp impressions can be examined to determine such things as:
Therefore, the examinations require original documents where possible, the rubber stamp/s allegedly used or suspected of having been used, as well as possibly other documents bearing known rubber stamp impressions for comparison.