Right now if a wiki page has referenced a image/picture, it is not visualizing the lack of the attached binary.
It would be great to add a image reference like this https://upload.wikimedia.org/wikipedia/commons/e/e4/Comic_image_missing.svg with the missing image name as a caption to let the user know, that he has forgot to upload a image

In following cases the images of a wiki page could be missing:

• you create a new wiki article, you already reference the wished image, and you later want to batch-upload all images
• you cleanup the current wiki pages, by copying some parts into new wiki pages, but you forget to re-upload the images again

In both cases the issue can happen quickly. Sadly if you miss to upload the images afterwards, you need a admin to determine where the images have been and to reupload them again.
This is not user friendly.