From what I understand in the first part of this thread, the discussion is about whether PageRank flowed to image files. From my experience, it doesn't
This should be relatively easy to check for any site that links to an image URL rather than an HTML page. Just check the toolbar PR for the image's URL, right? None of my sites linke to image URLs, so I have nothing that I can easily check.
If there is a PR value, then PR is being voted through that link. This means that other links on the parent HTML page (for instance, navigation) are voting a smaller portion of the total available PR to their target pages.
However, all that is based on the original PR model, and that model is long gone. What we now have has been called the "reasonable surfer" model and PR transfer is heavily weighted toward the links the visitor is more likely to actually use. In fact, given the data Google collects from Chrome users, I wouldn't be surprised if this weighting is using real click data for at leasts part of the assigned weight.
However, since image URLs only show up in Image Search and not organic rankings, it does seem that something else must also be involved.