Cheers mate much appreciated.
The main issue is not so much on desktops, but rather the effect it has on mobiles. Doesn't scale, takes up a big chunk of screen real estate, and makes it harder to see / get to / scroll to the main menu items. Kinda throws things outa whack.
Scaling a banner to suit (relatively) small smartphone screens may well be something between impossible and pointless.
I think the better option would be (if possible) to have it:
On desktops - display banner (perhaps an on/off option would be good here)
On mobiles - do not display banner, just header text as normal.
I think that would be the most practical solution. Whether that's easy or even possible to implement? Haven't a clue. I'm sure you'll let me know... I just hope you haven't torn out all your hair by then.... LOL
edit: One super cool extra feature would be if you could have a range of images and 'cycle' between them randomly - I.e. each time a user accesses the forum it grabs randomly one of 'x' images. Just a feature idea, nothing I expect you to take seriously....