Increasing availability of Unmanned aerial vehicles (UAV) and different software for processing of UAV imagery data brings new possibilities for on-demand monitoring of environment, making it accessible to broader spectra of professionals with variable expertise in image processing and analysis. This brings also new questions related to imagery quality standards. One of important characteristics of imagery is its spatial resolution as it directly impacts the results of object recognition and further imagery processing. This study aims at identifying relationship between spatial resolution of UAV acquired imagery and variables of imagery acquiring conditions, especially UAV flight height, flight speed and lighting conditions. All of these characteristics has been proved as significantly influencing spatial resolution quality and all subsequent data based on this imagery. Higher flight height as well as flight speed brings lower spatial resolution, whereas better lighting conditions lead to better spatial resolution of imagery. In this article we conducted a study testing various heights, flight speeds and light conditions and tested the impact of these parameters on Ground Resolved Distance (GRD). We proved that from among the variables, height is the most significant factor, second position is speed and finally the light condition. All of these factors could be relevant for instance in implementation of UAV in forestry sector, where imagery data must be often collected in diverse terrain conditions and/or complex stand (especially vertical) structure, as well as different weather conditions.