I need advise. I want to create web page, where users can upload their images, and on server side I want to put these images to prepared image template and show on page. Is it possible? Is it possible with GIMP scripting? Any ideas?
Unless you want something that exists only in some Gimp script/plugin (and even then, most of them are open-source...) using Gimp for non-interactive work is at best overkill and very often more complicated than strictly necessary.
Simple (and even fairly complicated) programmed image edits can be done with several libraries and utilities. ImageMagick is a nice toolbox to do image editing in shell scripts.