I recently discoverd that removing an image from a ArcGIS Hub Site page only hides the image. It is still attached to the page as an resource.
As my users frequently edit and update pages and the images on the pages, the page size started to grow and this became a problem when I had to clone a complete site and 500MB+ of data was copied.
I reached out to my local support and this was acknowledged as a bug, so hopefully, in the future, Esri will provide some means to manage the (image) resources of a Site page.
For now, I have a notebook script which makes it easy to get all the pages in a Site view all the image resources on a page and checks whether the image is used or not. In a final step, you can automatically backup and delete the unused images.
I'm sharing this here, because other users of ArcGIS Hub might be facing the same problem and maybe my script can help these users as well.
Have a look here for the script: https://arcgis.com/home/item.html?id=88695938832a4b748f8de78ad6658835