I am not a GMail user (and this note may illustrate one reason why), but my wife and some of our friends are.
A few days ago, I e-mailed some personal photos of my wife to one of our friends who uses GMail, and cc'd my wife. This was intended to be a one-time transmission for just their eyes.
But now, whenever either of them open any e-mail from me, on any subject, those photos appear in the right margin of their GMail screens, under "Recent photos."
This proved especially embarrassing to my wife when today she opened a business e-mail from me with a professional colleague watching, and the personal photo again popped up in the margin. She asked, how can Google justify doing such a thing? More importantly, how can she prevent it from happening in the future?
She tried an experiment: She located the message with the photos attached and invoked "delete this message." Then she found it in her Trash and invoked "delete forever." But still, the pictures show up under "Recent photos" when she reads any message from me. Even worse, if she clicks on any of those photos, the entire text of the message she supposedly just deleted forever shows up again.
She would like to permanently remove those pictures from Google's memory. She is afraid that Google will use them to illustrate mail to other GMail users who should not see them. I would like to assure her that this will not happen, but I have no factual basis for such assurance.