Not to be a stick in the mud, but you're using a copyrighted image as your logo without any attribution or acknowledgement of the original owner of the copyright (the Lego Group). You should probably fix that.
You're right! We put it up there when it was an internal project, it's probably time to take care of that. Taking it down until we found a correct way to do it.
I'm a copyright noob: would simply acknowledging the copyright owner be enough and fall under fair use, or should we not use it unless we get written permission?
I am not a copyright expert, however I am familiar with the Lego Group (the company that produces Lego toys) ... the set is pretty old (1986), which means they're not worried about making money off it. If you just stick a disclaimer after it that it's copyright 1986 the Lego Group, that's probably fine, especially since this looks to be an open source project, so you're not going to be charging people for something with their picture on it.
This page has what is very likely the original image: http://www.peeron.com/scans/7823-1/ Peeron.com has special permission directly from Lego to display the images, so if you wanted to be extra careful you could email dan@peeron.com and ask for permission to deep link to their picture (they'd probably say yes, the admin is a linux geek too). But honestly, a simple copyright disclaimer is probably fine. Lego won't reach out and swat you even if they do decide they don't like it, they'll just ask you to take it down.