Once you've quoted a post so that it's in the editor. Go to the image/gif/spoiler whether it is in a spoiler or not, then delete it. If you can't delete the image, then delete the whole spoiler.
The better way to handle quoting elements from another post is to highlight only what you want to quote which will cause a quote button to pop up, then use that quote button. This will only show after you have highlighted the specific material you want to quote.
If you do this ins
Quoting manners and a warning to this thread in general about content.