Digilib is a state-less web-based client-server application for interactive viewing and manipulation of images. It consists of two parts - the image server component proper, called "Scaler" and a client-side part that runs in the user's web browser. The users browser sends an HTTP request for a certain (zoomed, scaled, rotated) image to the Scaler server and the server returns the image data as an HTTP response. We must also take into account the client-side part consisting of HTML and Javascript code that has also been requested and loaded from a frontend-web server into the user's browser.