You are browsing the old Contao 3 extension repository. Contao 3 is no longer maintained as of June 2019! You can find the Contao 4 extensions on extensions.contao.org.
Extensions > pageimage
Set an image per page
After installing this extension, you can see a new field for each page in the page structure to set an image file. Using the appropriate frontend module allows you to show the image at a specific location in the frontend. If there's not image for the current page, the parent page's image can be shown.