In the frame of smart city initiatives, map-based web applications (WebGIS) are distinguished by the complexity of client-side implementation and high load on web servers. Web-map applications provide non-typical web content usually visualized by JavaScript code. For such applications, higher-level advanced approaches to quality of service (QoS) assessment are required. In this paper, a method based on the estimation of users’ interest in a web page and the information quantity provided by a web page is introduced. In order to implement it, a proof of work (PoW) concept is applied for verification of real users. Moreover, a novel metric is introduced to calculate the information quantity provided by web pages. PoW is used for verification of real users and distinguishing them from bots. Additionally, it can be utilized for balancing of web server load. For monitoring of web pages, an image-based approach is introduced. Web pages are rendered into raster images. A number of metrics describing an image are calculated. This approach allows users to compare and track various web pages, including rich web applications providing complexWebGL content. Several web services utilize the developed solutions. Analysis of harvested data proves the effectiveness of the proposed solution.