Looks like the footer’s background - see More button on the Footer tab of the page format.
… or not, since the image (and text!) are outside of the footer’s text area; maybe it’s not a footer’s data, but a frame with image and caption, moved almost out of the page? Use navigator to check existing frames.
Also it’s good to have Formatting Marks enabled, to see what is actually present in the document, including whitespaces, newlines, etc.