We have many pages that are linking to an image in the Image Library. When we try to update the image, the image is not updated on the pages.
By updating the image with a new image file name, it essentially just adds a new image in the FTP server, but your pages are still pointing to the old image.
To successfully replace the image, you'll want to be sure to you do not delete the original. Instead, name your new image exactly the same as the old image and then follow the steps to update the image.