Originally Posted by roger64
To come back to my first idea, is it possible to enhance the div containing the image with some id tag so that it can be displayed in the TOC?
You don't need to "enhance" any
of the (x)html or css to display whatever your heart desires in the ToC. As Jellby already mentioned earlier; simply modify the toc.ncx file manually. All the h tag and "visibility: none" trickery is only necessary when you want to generate a ToC automatically
using other tools.