I use google+ for various groups and they send me html-emails, some of which
show graphics, ie screenshots of their mobile desktops, and I would like for
those graphics to be auto-downloaded when I open the email. But how please? I
haven't found any way of doing it in gnus whilst googling for it.

Currently I get what you see in this screenshot, if it makes it on to the list?
Just the html parts of the text are highlighted in a light grey colour, against
the black background of my emacs theme.