I know that there are even some web-resources exist which allow you to get a preview of a web-site 'as it looks in a certain browser'.
I only need view from any browser as an image. Is it possible to get that image without people involvement? Can I get it without system programming, just by means of pure java/python/asp.net?
UPD: http://browsershots.org/ is an example of described web-resources.
The tools I know of that does this - really "just" launches a browser (programatically of course) and takes a screenshot of the contents of the browser and saves this in an image.
I think no matter what you do, you will have to find a way of doing something like this. If you by system programming are refering to OS API calls, then I think you will be out of luck. You might be able to get a third party library that can do this for you, but then that library will simply be making those system calls instead.
I see now others have posted links to places that might prove themself useful to you as well. Without having looked at the links, that would probably be the easiest and best way to go.
Good luck
If you're using .NET, it is possible to do this using the DrawToBitmap method of the WebBrowser control (example here). However, as you'll see by the last comment on that example page, it doesn't work with Flash, and it's a bit 'temperamental' with sites that use complex Javascript for rendering.
I think your best bet is to do as others have said and use a third party thumbnail provider. I haven't used it, but http://www.thumbshots.com/ looks good.
PageGlimpse is a service providing developers with programatic access to thumbnails of any web page.
It has API based on REST protocol and some documentation.