I've tried setting image-dired-thumb-size (and/or image-dired-thumb-height image-dired-thumb-width) and it has no effect. I've set it globally in .emacs and in various mode-hooks, all to no avail. The default value is 100 and I change it to 256 and the thumbnails are still 100. Inquiring the variables says they are 256.
These variables seem to have no effect. Is there a way to make this work?