I want to use the Stack Overflow logo as an image on a blog post about this site. What are the rules on using it? Can I use it in any way? Can I chop the words out and just use the image, or must I keep it intact?
It is a trademark. The purpose of trademark law is to prevent consumers from being misled as to the origin of a product. So if you were making a product, and you used the name Stack Overflow or the Stack Overflow logo in your product or its advertising, in such a way that would mislead some consumers into thinking that your product was Stack Overflow, you would be violating the trademark and this would not be legal.
For example if you started a website called "Stack Overflow News" and used the logo, that would create confusion... people might think that the site was a part of Stack Overflow or was officially endorsed in some way. If enough people were reasonably confused as to the origin of your site, it's a violation.
The logo image itself is copyright. Copyright is different than trademark. Ordinarily you couldn't copy it. But if you were writing a news story or blog post about Stack Overflow, reproducing the image would almost certainly be considered "fair use" and thus permissible.
If you were writing a blog post, say, about Stack Overflow, for example, and the blog post was a description of the site, maybe a review, and there was no possibility that anyone reading that blog post would think that in some way YOU were Stack Overflow, then using the logo would be fair use under copyright law, and allowed under trademark law because you were not using it "in trade."
Trademark law is a lot more complicated than that, so you'd have to consult with a real lawyer if you thought you were doing something iffy.
There is a creative commons link on the bottom of every page, but it's unclear whether that covers all content or only question/answer content. For lack of a clearer definition, you can probably get away with using the "all content" definition (pending remarks from Jeff Atwood or Joel Spolsky, of course). Also, even if the site founders intend the logo to also have a CC license, the graphics designer they hired to create it may still have a say in that.
Finally, the CC license would only cover copyright. The logo is being additionally used as a trademark, and while it's not registered (at least, they don't use the little ® symbol), you could still have issues just throwing it anywhere.
As long as you don't do anything that could cause 'consumer confusion' — where a someone might accidentally think some service provided by you is in fact provided by StackOverflow — you ought to be okay in that regard.
I'd just go ahead and use it. If you are blogging about this site I think it is fair game given the CC thing and lack of TM or R logos. If they have a problem with it they can contact you.
Given that you plan on using it to link/post about SO then it is probably appropriate.
I'd probably put something int he post about the logo being the property of SO or taken from SO. (Can't say it is registered TM because I don't think it is)
Caveat: I am not a lawyer.
Common sense says: without explicit permission, don't do it - the logo is intellectual property that does not belong to you. Using it implicitly implies affiliation with and/or endorsement by Stack Overflow, which you do not have. Using it without permission invites a lawsuit. Whether the logo is trademarked or not is irrelevant. Would you use IBM's logo on your web page without their permission? Of course not. The same applies to any other business.
Best advice: follow Jeff and Joel on Twitter and just ask them for permission.
OK, so my comment on Joel's post got long, so here it is as an answer :)
I want to use the stackoverflow logo as an image on a blog post about this site. What are the rules on using it? Can I use it in any way? Can I chop the words out and just use the image, or must I keep it intact?
OK, so you are writing an article about Stack Overflow. You are not in any way claiming to BE Stack Overflow, just writing about it. Then I would say you are good - there is nothing that can OR should be done against you by Stack Overflow Ltd. It's the same as if you write about Microsoft, you can use their logo, for example, as an illustration to go with the article.
I'm not sure on the legalities about having to file for TM protection, but general use says you are good - the same as general use (or whatever the legal term is) says that Stack Overflow Ltd have the rights to their own logo, even if they haven't officially (tm)'ed it.
Now, if you were using it as the logo for your blog or company, then: hell no. Even if your Stack Overflow Ltd was involved in something like paper stacking machines, it's still a confusion for a customer - just think about Apple Computer vs Apple Corps (the Beatles recording company) or iPhone (Apple) vs iPhone (Cisco). Both of these were settled in and then out of court. I think Apple lost (that is, had to pay) both, and it cost them a few million. Also, why is the Apple TV called Apple TV, and not iTV? Google "eye TV" from Elgato, which is an Mac-only TV tuner....*
So yeah - if you have a blog post about Stack Overflow, and want to put the Stack Overflow image inside the post: I can't see how Stack Overflow Ltd (ie, J and J and G and .... damn it, what's the other guy(s) names?) would have a reason to do anything "to" you. Even if your blog post said "Stack Overflow sucks munkeys, d00d". Are you legally allowed to do it? I'd say so, tho IANAL, and the worst that would happen is you'd get an email from J and J asking you to remove it.
I would try to use the image as-is if you can, BUT if you can find just the logo anywhere (it's in the favicon for example) then they have used that on it's own, so it's logical that you can too...
- I think in this case, Apple decided not to turn on one of their more popular 3rd party vendors, so they just chose a better (IMO) name for the product. And they would have lost in court (Elgato Systems has been around for ages).