We developed an online system for estimating dietary nutritional content. It also had the function of assessing the accuracy of the participating dieticians and ranking their performance. People who wished to have their meal estimated (i.e. clients) submitted images of their meal taken by digital camera to the server via the Internet, and dieticians estimated the nutritional content (i.e. calorie and protein content). The system assessed the accuracy of the dieticians and if it was satisfactory, the results were sent to the client. Clients received details of the calorie and protein content of their meals within 24 h by email. A total of 93 dieticians (71 students and 22 licensed practitioners) used the system. A two-way analysis of variance showed that there was a significant variation (P=0.004) among dieticians in their ability to estimate both calorie and protein content. There was a significant difference in values of both calorie (P=0.02) and protein (P<0.001) estimation accuracy between student dieticians and licensed dieticians. The estimation accuracy of the licensed nutritionists was 85% (SD 10) for calorie content and 78% (SD 17) for protein content.