Resumo. ABSTRACT New ways to obtain information on sedentary behavior (SB) have recently been explored. This study aimed at assessing the self-reported posture agreement by using the Ecological Momentary Assessment (EMA). The images were sent by an observation protocol created in a form that would be answered via the mobile phone of young adults. The bank of images was provided by 41 university students. Such images were obtained from a project carried out in 2019, which was based on the taxonomy of sedentary behavior. The following positions were assessed: sitting, lying/reclining and standing, comparing the images provided with the self-reported SB by using EMA, which was collected via cell phone. The agreement was assessed by two researchers independently. Data analysis was based on descriptive statistics, Student's t test, chi-squared test, and Cohen's k in SPSS 25 with P<0.05. The inter-rater reliability was strong/substantial, that is, 87.6% (rater 1; k = 0.696) and 88.6% (rater 2; k = 0.720). The image observation protocol created in an electronic form could discriminate the behavior adopted by the participants, as well as it could be used independently, only for recording EMA and/or the image/photograph.