After an image is uploaded, its name is shown when you mouse over:
It doesn’t make a lot of sense for users nor for SEO.
It would be good if moderators and post authors were able to change that name after upload.
NB. It doesn’t make a lot of sense to ask users to rename images before uploading because:
They often do screenshots and the file name is given to the screenshot automatically and copied to the clipboard.
The often just copy a URL to an existing image on the net and just insert it.