In photography, the dynamic range (DR) is a distinguishable brightness range and is determined by the analog-to-digital converter (ADC) and signal-to-noise (SNR) performance of the sensor. Recently, many various HDR strategies have been introduced to obtain high DR beyond these hardware limitations. However, since camera manufacturers set these HDR algorithms to operate differently by considering the situation, it is necessary to evaluate the quality of images taken in various situations for objective evaluation. In order to quantitatively measure the DR, we should know both the actual luminous intensity and the SNR of the picture. However, it is difficult to measure the two information in general-scene photos without charts. To overcome these problems, in this study, we propose a method to measure the DR of a natural-scene photograph by reconstructing radiance map and specifying the pixel value at which the SNR reaches 12dB. Using the pre-calculated radiation and SNR information, we measured DR of photos without using a chart, and demonstrated that HDR images have higher DR than standard DR (SDR) images.