In recent years, the use of unmanned aerial vehicles (UAVs) that has been introduced to UAVs has been widely used in surveying engineering under the name of UAV photogrammetry. Different urban and non-urban scales on different scales provide the conditions for examining and evaluating the geometric accuracy of these high-resolution spatial images in the production and delivery of large-scale maps and coverage scales. One of the most important geometric parameters in UAV images is the determination of the spatial resolution, which is known as the criterion for detecting the smallest distance between two adjacent objects that can be distinguished in the images. There are several ways to accurately measure the spatial resolution of images; in this study, the Siemens star was used as one of the most widely used artificial targets in measuring spatial segregation. The purpose of this paper is to provide an automatic method for detecting the radius of ambiguity and calculating the spatial resolution limit in images taken from UAVs. The results of this study showed that firstly, according to the flight altitude and the amount of blurring of the image, the Siemens Star Target should be used with appropriate dimensions and number of arms, and secondly, the rate of reduction of image resolution in the tested drones was between 1.2 and 3.7.