Best practices on images directory naming

Anybody knows best practices about image directory places? I whish to
maintain this directory structure:

        maindir/
                main.xml
                subdir1/
                        subcontent.xml
                        image1.png
                subdir2/
                        subcontent2.xml
                        image2.png
                ...

but don't know if I can set stylesheets to FO processor or HTML look for
images on the right dir without adding then to the fileref path.

Any advice?

-- 

        A. Ismael Olea González
 
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