Deleting files from the "manage images" folder

Upon uploading a small animated gif for a post, a non-animated jpeg appeared instead, along with a thumbnail directly beneath it.

Not sure what the purpose of the thumbnail was, but found no means of deleting it. Even after removing the primary image from the post, the errant thumbnail remains.

I was able to close one in the managing images side folder, but the main images have no delete option. What gives?

Also, just curious, but l what advantages do the text frames provide? I noticed numerous posts are triggering these separate text windows to appear, and often require additional scrolling to read.

Is there a benefit to them?