Although LinkedIn is primarily a business networking site, it’s still considered social media. That’s part of the reason having a profile photo and, with the new user interface, a background photo too.
That said, LinkedIn is not Facebook. Which means your photo needs to be recruiter and employer ready.
Despite this, I often seen inappropriate photos used in LinkedIn profiles.
I don’t mean the obvious mistakes like party photos, although I’ve seen them, it’s photos that people have put some thought into.