The problem is that images embedded in emails (such as when sent from an iPhone) are not shown "properly" in Gmail in OS X Safari, i.e. they are shown at probably 100%, which is almost always oversized for all but huge screens.
The ideal situation would be some kind of zoom-out function, so my Mom can see the whole picture at once. However, there seems to be no Gmail feature for that.
A workaround would be to cmd/two-finger-click the image and "Open in new tab", where the image could then be manipulated at will. Instead, Safari opens an empty new tab, downloads the image, and auto-opens the image (from the Downloads/ folder, since it's a "safe file type").
How do I get the ideal situation to work?