Laser printers, ink jet printers and thermal printers can all provide a huge amount of evidence. Usually the question is whether or not a specific printer or photocopier has produced a particular document. This question can often be answered conclusively - i.e. the printer can be identified to the exclusion of all others.
Linking printer hardware to evidence
It is also possible to provide relative dating of printed documents by comparison with a range of printed material known to have been produced over time on the same printer.
Examination of printed documents can also show that a document has been altered, for example if an additional paragraph has subsequently been added to a document or a page is replaced with another containing different information.
It is also possible to provide an indication of the printer make, model and sometimes serial number just from the printed document.
Even without the source printer, it may be possible to demonstrate that two documents were both produced using the same printer or photocopier.
It is crucial in a printer case that the original documents are provided. A photocopied document will hide many of the features put on by the original printer (although there will be features applied by the photocopier).