Dammit, Jim, I'm a writer not a lawyer.
http://lifehacker.com/193343/ask-the-law-geek--is-publishing-screenshots-fair-use
I take my own screenshots all the time and I've never had a problem with it, although I don't publish the material myself - it's published by the company I work for. Our software requires a certain amount of server configuration. Those servers typically run MS operating systems, and therefore there are instructions for configuring those operating systems to work with our software. I've never been informed that this is a concern by any legal department (although they have supplied me with EULAs and copyright pages).
I suppose this is different than what AW Admin is talking about and what you want to do. You won't find my manuals online or in a bookstore. They are only ever delivered with the product or when requested by a customer.
There are times when I end up with a special entry regarding ownership of certain materials. These typically involve licensing agreements for the use of specific Codecs or protocols and occasionally hardware. Sometimes I am informed to leave certain material out of the docs altogether. And sometimes I have to edit screenshots to remove features that are only available to specific users who have purchased specific licenses.
Over the eighteen years I've worked in technical communication, none of the companies I've worked for have ever been concerned with my taking screenshots of 3rd party software interfaces required to explain how to configure or operate our deliverables. It should be noted, though, that I am required to state the name of the company owning or producing the software on first instance. For example, the first time I mention a Windows server I have to state "Microsoft Windows Server 2012" and thereafter I can refer to it as 'the server' or 'Windows Server 2012' without mentioning the name. This is a pretty standard rule. "Microsoft SharePoint" first, then 'SharePoint.' Etc.. I would certainly abide by this rule and I would probably advise placing a disclaimer somewhere on your site identifying the owners of the different screenshots. Some docs keep a list of figures that identify them. This always seemed overkill to me (since users never view it) but maybe it exists for legal reasons.