Be mindful of copyright when downloading material from the Internet.  Just because a work is posted on the Internet does not mean that it is in the public domain, or that the owner of the copyright in it has given you permission to make copies or distribute the work to others.  Note, too, that material may have been placed on the Internet without the author’s permission.  Fair Use principles (see below) may apply, but you need to go through a fair use assessment to decide that.  There is material on the Internet that is either in the public domain, or is publicly licensed (e.g. CC licensed), but you must confirm the status of any material you hope to reuse. 

Similar concerns apply when uploading material to the Internet. It might be perfectly acceptable under the Fair Use doctrine to include graphs from various articles in a paper written for class; it is probably not a fair use, however, to publish those graphs to the world by posting the same paper on the Internet.