The invisible facial flushing in dengue infection and influenza can be detected and visible by the Manote and Matinun (M&M) technique using PC program and smartphone app. The unique patterns of facial flushing provide a clue to the diagnosis of dengue infection and influenza. To analyze the facial flushing areas in dengue infection and influenza compared with other causes from the single face photo by smartphone camera app and apply the enhanced single face photo as a novel screening tool for diagnosis of dengue infection and influenza. The patients with acute febrile illness were classified into 4 groups of different underlying causes as other causes, dengue, influenza A and influenza B respectively. The single face photo was enhanced with the Rock Art Enhancer app using for Android smartphone in 3 steps modified from the Manote and Matinun technique and further analyzed with the ImageJ program with Color Inspector 3D plugin. The patterns of the facial flushing areas were differentiated into 3 categories, as no facial flushing, localized facial flushing and generalized facial flushing. The analysis of the facial flushing areas was calculated in percents of primary and secondary facial flushing areas (1 FFA and 2 FFA). The sensitivity or "true positive rate" of 3 steps modified Manote and Matinun technique for all tests in dengue, influenza A and influenza B group is 96.8% (94.2% for all patients). The 97.8% of dengue group tests (94.7% for of dengue patients) could be detected the facial flushing either localized or generalized pattern. The upper cut-off points that helps distinguish from neither dengue nor influenza to either dengue or influenza is approximately 20% and 9% in the primary facial flushing areas (1 FFA) and the secondary facial flushing areas (2 FFA) respectively. Although the generalized facial flushing patterns were found in dengue (66.7%) more than in influenza (50%), but we could not distinguish between dengue and influenza, depending on two different patterns of facial flushing (no statistically significant differences, P = 0.09). The enhanced single face photo with 3 steps modified Manote & Matinun technique is useful as a novel screening tool to distinguish other causes of acute febrile illness from both dengue infection and influenza. The upper cut-off points in both primary facial flushing areas (1 FFA) and the secondary facial flushing areas (2 FFA) help for the recognition and diagnosis either dengue infection or influenza. Because it is useful and effective as well as economical and available so it should be suitable for a novel screening tool in the diagnosis of dengue infection and influenza, including for the application of telemedicine in the future.