I have had similar problems with placing full-page images into Indesign. Here is what I came up with.
I create a paragraph style and name it “invisible.” The type is very small, 6pt, centered on the page, and I make it magenta so it shows up on the page. Using this invisible style I type the description that I want to appear in the TOC but not on the page with the image, such as “Title Page,” or “Map of Spain.” When I create the TOC, I add the paragraph style ïnvisible” to the other styles I want the TOC to display, such as chapterNumber. Then I place the image on the page under the “invisible” paragraph style and anchor the image to the “ïnvisible” text, with äbove-line anchoring, centered, with a negative Y axis setting. (The only setting I can get to work.)
Then I export to epub, open the file in Sigil, add this to the css for the invisible paragraph style: visibility:hidden;. This makes the text disappear, but the words that I type using the invisible style still show up in the table of contents.
I am new to everything epub and have spent hours trying different things, so I was very happy to come up with this workaround. Is there another way to get an image to show up where you want it without anchoring it to text, even if you don’t want the text to appear? I would use a similar paragraph style even if I didn’t want it to be referenced in the toc.