Any images you drag and drop onto TiddlyWiki are stored as base64 encoded and that is the problem.
- neither browsers support "copy as images" (to clipboard)
- nor Microsoft Office supports "paste as images" (from clipboard)
...whereby any base64 encoded datauri's would be automagically converted into their image representation.
So, the best chance you have is to not drag and drop images onto TiddlyWiki, but to store them into some
img subfolder and then display them in TiddlyWiki, e.g. using something like
ximg. Then you would have actual images that you can later copy & pasta as you're used to.