They're astonishingly poor at data ownership. When they started Dropbox Paper, a note taking web app, they sent the inline images to a different web domain. The image, doing so, became publicly visible to anyone knowing the URL! They did this without explaining anything to the user.
They also did not clarify who owns the copyright of these images sent to an apparent third party company.
Seriously, Dropbox's user privacy and copyright management is incompetent and untrustworthy.