Wonderful, each time you update phpBB you will have to start all over again
That's besides the point. And anyway, placing it a personal image in /images makes just as little or as much sense as in a style folder because an update or upgrade may replace these directories (depending on how it's done - the update/grade instructions do mention how to avoid that luckily).
Allright with you
And I agree with that, but in this particular case just mentioning that the image has to be placed in the images folders, doesn't help in explaining why his placement of the image didn't produce the expected result.