[DSpider]

Well, basically you cut the image, place the cursor at the beginning of an empty line and paste it there (except with line spacing set to "Auto"). This inserts it as an in-line image, but it's also a paragraph in its own right. And paragraphs can be styled with Paragraph Styles. Then you generate a TOC based on that style. Hmmm... But I'm not sure InDesign works that way... Without text, that is. If you still can't find a solution, a dirty hack would be using very small text (1 px), or invisible text (maybe set to the "Paper" swatch colour?) before each image. But then again, you can always edit the code, like dgatwood suggested, in Sigil or something.