I recently found out that Nautilus (Ubuntu 12.04 at least) can show thumbnails of files of non-image formats, for example (data grapher) grace files (.agr) shows a small version of the graph contained in its data. Obviously, there some library or script that is processing the file, making the image, and allowing nautilus to show a small version of it.

This made me think that in principle any file that potentially can be processed into an image can serve as a Nautilus thumbnail.

For example, a .tex file (which can be converted to .pdf) or a gnuplot script can be displayed as a thumbnail when possible.

In the case of .tex file, the correspoding .pdf can be created by the command pdflatex file.tex.

The question is, how can I tell Nautilus to create a thumbnail for an arbitrary format and how do I specify the commands to do so within Nautilus?