zombie84 said:

I'm thinking of re-designing the website, to be a bit more interesting to look at. I'm not sure how I feel about using official pictures since I am making money off a product on the site, and Lucasfilm have so far left me alone. But I feel like there should be something a bit more eye-catching. Any thoughts?

What about some of the McQuarrie concept art? I checked out his official site and there are a ton of pieces that are iconic in their own right.

No doubt Lucas has claims to owning all that artwork (just as he does with the word droid), but there is this statement in their disclaimer section;

All original content of this site, both graphical and textual, is the intellectual property of Ralph McQuarrie, www.ralphmcquarrie.com, and Dreams and Visions Press unless otherwise indicated.

Perhaps some of the early concept artwork isn't owned by Lucas. You're a published author, not just some nerd with a blog. No harm in contacting the company handling his estate - on a professional level - and looking into what they may let you use legally.

May even be able to work the piece as the cover of your next printing of Secret History.