Looking for accessibility and tool tip options for images in Pages

I have some icons in a Pages document and don't want to clutter the page with a caption for each icon, but would like something to display if the user hovers over it (like a tool tip). I also link the icon to a bookmark in the document. I expected the bookmark name to show up when I hover over the icon (like it does with a web link in the pages document when it is exported as a PDF).

I tried to figure out how to add alt text or a tool tip to the image but couldn't find anywhere to do that. On the format pane for the image there is a description box but I can't figure out where that is used.

I am ultimately exporting the document to a PDF where the bookmarks are used to navigate around the document and the links take the viewer to a webpage.

For accessibility I've been using alt text on our website and in PowerPoint presentations and expected to have that capability in Pages.