The problem: drag-n-drop an image into a gmail draft will embed the image.

The solution (for a computer only):

1. (do not drag-n-drop. No known way to convert the inline image into attachment.)
2. In the draft editor, find the bottom row of icons like send, attach, insertSignature,,,
3. find the icon for insertImage
4. click to get a pop-up
5. look at the bottom right .. Inline vs asAttachment. Choose the latter, before adding a photo