By default the image displayed for a page in a link to that page is the first image that can be found on that page, or on a child page.

The @icon directive can be used to override the link image used, or have a link image where there is no image on the page itself.

So for example the Events style child page source file has:

@icon ../../apple.jpg

in it. The apple image appears on the Events style page but not the child page itself.