Place a scale, preferably a right-angle scale (or ruler or tape measure) alongside and parallel to the long axis of the impression, not across the middle. The impression should also be viewed with oblique lighting to see if the impression becomes more visible. Begin by taking photographs in ambient light or with normal flash. If using a digital SLR camera, the image should be taken in the. Regardless, these impressions should be photographed before any collection or attempts at lifting the impression occur. Two-dimensional prints can occur in two ways: when debris is transferred from the footwear or tire onto a clean surface it makes a positive impression, or if the footwear or tire takes a substance away (ie: an impression in spilled powder) it makes a negative impression. If another type of object leaves a two-dimensional impression, the collection techniques would be the same as with footwear and tire impressions. It should be noted that other objects, such as fabrics, can also leave two-dimensional impressions. This can be accomplished by covering with boxes, marking areas with cones or crime scene banner tape, or by posting a guard. All impressions must be protected from water, wind, equipment, and foot and vehicle traffic until they can be recovered. Most of the time, two-dimensional impressions are fragile and, therefore, should be carefully protected and processed as soon as possible to prevent degradation. Two-dimensional footwear and tire impressions can be made in any type of substance that can be transferred, such as dust, soil, blood, foodstuffs, etc.
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