Internet of things (IoT) is increasingly useful in connecting network of devices on the internet. A popular need of IoT in the industry is to measure the level of the liquid in a faraway tank of interest. The traditional measurement method uses float, pressure or ultrasonic sensor and provides reliable results. Nonetheless, the disadvantages of traditional methods are that their range of measurement is rather short and their maintenance on the field is also difficult. To solve these problems, we propose a novel method that combines the image processing algorithm with Node-Red IoT systems. The original idea of this paper is to use the image of the ruler on the tank for measuring the physical height of liquid level in standard units. Our experimental results on real-time collected images via IoT live-streaming show that our proposed method is very fast and robust with different size and shape of different rulers. Our method is also accurate enough to facilitate the application of liquid level measurement in practice.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.