In many cases it is fine to use articles from the open web. That said, there are a number of instances where pdfs (especially) are freely available online and they shouldn’t be there. Copyright compliance officers advise not to use materials that look like they were posted illegally.
Link to OA articles rather than embedding the pdf into the course content. This not only provides the journal publisher with a method for gathering stats on how their publication is used; it also has the potential to effect impact factor and could further encourage the OA movement.
Note: CC licenses can sometimes apply.
Creative Commons licenses (CC licenses) give everyone from individual creators to large companies or institutions a simple, standardized way to grant copyright permissions to their creative work.
A number of licenses exist with varying levels of protection.
Licenses, contracts, and other forms of intellectual property can take precedence over exceptions.
In general, library subscription databases delivering periodical content allow for certain type of use:
Create a permalink to material from within a library's databases and post it in Blackboard.
Request an article via document delivery for your own personal scholarship and use.
Download an article from a library database and post the pdf in Blackboard.
Request an article via interlibrary loan to post in Blackboard.
-- .edu websites: just because another university has posted it, doesn't mean it was lawfully posted.
-- If material seems like it should be licensed, there is a good chance it is!
Open Access journals are making it trickier to tell how content is licensed. Be sure to check the publisher's website.