Before you do anything with impression evidence, you need to photograph it. This is a key step that you can’t afford to miss. If something goes wrong during the processing and you forgot to take photographs, then you’ll be left with nothing. So get in the habit of taking your photographs first, and remember to use the proper labeling, lighting, and scale with the evidence. For example, if you’re working with tracks, you need side lighting, which creates shadows that provide 3-D depth and allows you to see the details of the evidence. Also, you should always insert the scale at the same depth as the track impression—otherwise, if you place the scale on the surface, you’ll throw off its accuracy.

From: Impression Evidence by Dick Warrington