A topic I actually know a little about. Owned a web hosting company and built online databases for 15 years, still do a little of it. If it is posted on the internet and not password protected (in other words, you don't have to have a username and password to access it) then you can legally link to it from anywhere else on the internet. The key here is the word "link".
- You CANNOT post a copy of an image or video from one site to another. Quoting text is a whole other matter.
- The link must take you to the originating site. So a link to a Stahls video that takes you to their website or another host where Stahls has posted it (youtube, etc.) is perfectly legal. These types of links are usually encouraged as they drive traffic to their site and boast their search engine rankings.
- If the link is to a static page then the link has to be descriptive text or the URL of the page it's taking you to. With written permission the link can be a screenshot or graphic.
- If the link is to a video then it can be descriptive text, URL or a screen shot from the video.
- The owner of the content (website, image, video, etc.) has the right to request you remove the link. If for some reason they request you remove it, you must comply immediately. This usually happens if the content of your site goes against the image the content owner is trying to project. So if you have a site dedicated to wild game hunting, the American Vegan Association might ask you to remove the link to their content.
- If the owner of the site you are on asks you to remove a link to another site you must comply. For instance, USCutter has the right to ask you to remove (or remove it themselves) a link to one of their competitors on this forum.
In physical world terms, if someone owns a custom car and keeps it in the garage, you have no right to go peeking in the windows or telling others to. If they park it in the driveway, you can drive by and gawk all you want. You can tell your friends where it's parked so they can drive by. But you can't drive it to your house.