I am not a doctor, I am a photograher so if I don't feel well, I see a PHYSICIAN! I am not a lawyer, so I consult a LAWYER when I have an important legal issue or question, I don't count on "Dr. Google or Google, and Partnersl Attornies at Law"
kinda thing. I mean a real LAWYER!
As a commercial photographer, I am somewhat familiar with copyright law because I have to deal with related issues in various contractual agreements with clients as to usage, licensing, ownership of images, etc. At one point in time, I had just about memorized Section 55 of the International Copyright Act and included references to it in my contracts. Over the years, however, times have changed and things have become more complex. Digital, imaging, social media, and the Internet in general, all have added to the complexities. Besides there are differet laws in various jurisdictions.
Dispite my experience, I would never assume to advise any photograher on these legalities, and the last person I would ask is another photographer. I am sure some photographers are significantly well-versed in copyright issues and more so than I am I also know that there are many who BELEIVE they know it all and operate on a lot of mythology, and old wives' tales and feel they have rights and privileges that they do not. They espouse false or erroneous information, not only about copyright and intellectual property issues, but privacy matters, shooting on private property concerns, and lots more. The star out sayig..we have the right to... and end up on the receiving end of a lawsuit or worse.
As for this forum, social media, etc. whatever you post there is at risk of unauthorized usage. Even if you have iron-clad legal protection, how are you gonna monitor the WORD-WIDE WEBB and enforc your rights? Do you have a law firm on retainer? The only advice I can offer in good faith is not to post anything that you fear will be copied, alterd, messed with, stolen, or in any way used against your will or better judgment. If you regularly sell your work commercially, as art, as a contractor, whatever, it is wise to consult will a LAWYER or law firm that is familiar with copyright, intellectual property, patent and trademark, and contra law.
You do not need to go to a lawyer for every contract or transaction. If your lawyer can familiarize you and set you up with some standardized contract forms, licensing agreements, etc. that is a good start.
Original question.
I would NEVER download, display, or do anything with anyone else's work without permission- not only for LEGAL implications but for a moral reason and common courticy. If I leave an image enough to want to use it as a screen-saver, hang it in my office, use it for teaching or training, or whatever, I owe it to the maker to buy it or at the very least get their blessing. I will NEVER represent it as my own work and make certain the maker gets credit!