The effect of perspective distortions on the size of the shoe sole footprint

In expert practice, traces recorded in photographic images are increasingly becoming objects of research during trace examinations. The fundamental criterion for this kind of objects is compliance with the techniques and conditions of shooting, which allows one to obtain informative photographic images of traces with minimal perspective distortions, when studying these images will make it possible to make the necessary measurements on them, recalculate the actual dimensions of the depicted trace, the sizes of its elements and individualizing features. However, in reality, when we are conducting trace evidence on photo images, in the most cases geometric and dimensional distortions of traces caused by peculiarities of optical systems and/or violations of the rules of detailed (scale) shooting of fixed objects are not taken into account. The presence of geometric distortions were formed because of deviations from the rules of detailed (scale) imaging. It does not allow to objectively assessing the reliability of the features displayed in the trace, which excludes the possibility of solving identification tasks. In order to establish the influence of optical distortions on the display of general and private features, the article describes the results of the conducted experiments on obtaining images of footwear footprints using a digital camera. According to the results of the conducted experiments (on the example footprints) the author proposes a universal calculation that helps to establish the size of the object under study, recorded with a digital camera, taking into account perspective distortions, the result of which is as close as possible to the true size of the object of study.