How can I know if I can modify/copy resources on this website? I was visiting a website/forum, and I saw that any content belongs to their respective owners. Does this mean I cannot copy/reuse/edit source-codes or other resources/contents the users are posting? Assuming I'm a moderator, does this mean that I can't even edit some posts in case of spam, and other? What will the penalties be if someone violates these rules?
The notification that you saw is not useful legal information for you: stuff always belongs to whoever owns the stuff. It might be interpreted as saying "it doesn't belong to us", but you can't count on that (it's virtually guaranteed that at least some of the content there is owned by the website owner). A more informative statement would be "You will have to get permission from the content owner to copy their stuff", and "We're not going to spend time figuring out who owns what". You could read the terms of service (try this with Stack Exchange) to see what the site tells people. The TOS here says that if you contribute anything, it "is perpetually and irrevocably licensed to Stack Exchange under the Creative Commons Attribution Share Alike license". You can then look up what that license says and learn what that allows. Websites are kind of tricky, though, because it's not hard to change the wording of a TOS, and you need to know what specific TOS was promulgated at the time a particular contribution was unleashed. Usual practice is to think it through carefully and not frequently tweak the TOS, but it's not illegal to change the TOS. Note that copyright law does not prohibit you from using other people's stuff, it prohibits you from copying. The distinction is clearer when you see a post that explains an algorithm with actual code, you read and learn and make use of that, but write your own code. As a user out there, if there isn't a clear indication that stuff posted is there for the taking, under some public license (as is the case with SE), then getting specific permission to copy, from the owner of the content (possibly untraceable), would be necessary. Now assume that you're a moderator or site-owner of some forum: presumably (hopefully) you have a TOS that addresses that situation, which says that moderators have the right to edit or delete content at their sole discretion, and also you say what kinds of posts are prohibited. Such an statement is not absolutely mandatory for all things, but it may be necessary to avoid litigation over some acts. One one end of the spectrum, it would be illegal for a forum to host child porn, stolen credit card numbers, or protected digital content. If a user were to post such stuff, the site would need to eliminate that stuff, and the poster could not legally rely on an argument of the type "That's my stuff, you have no right to mess with it". On the other hand, if a forum actually requires paid membership, then there may be a strong contractual expectation that the user is getting something of value, so you would have to watch for statements that could be interpreted as broad permission to put stuff out there without any interference. (For instance, a file-hosting service would have only minimal restrictions on content, aimed at protecting their own legal interests; whereas a political-advocacy site would have maximal interest in prohibiting the expression of views counter to the cause). Thus the SE TOS has you "grant Stack Exchange the perpetual and irrevocable right and license to use, copy, cache, publish, display, distribute, modify, create derivative works", which allows moderators to correct typos, delete offensive wording, and obliterate entire posts. If a site fails to have any such clauses in their TOS, then it might be a matter that has to be settled in court, whether they have the right to eliminate "spam" (i.e. advertising for a service, especially if the reason for getting an account was to provide an advertising platform). In light of the limited use sanctioned by the TOS, per the below comment, legal copying will be quite limited. However, "fair use" a situation where copying is allowed, regardless of what the TOS may say. (You could be banned from the site, but you could not be sued for infringement). Fair use was invented precisely so that people could make comments like "Jones advocates an absurd law, saying '...[quote from Jones]...'". Thus you can comment on a post and quote the relevant part ("The lines '[... quoting the code ...]' results in an infinite loop"). See the Fair Use FAQ for more details.
You are asking the wrong question. It should be: When you have downloaded the content and metadata, what are you allowed to do with it and what is forbidden? Somebody owns the copyright to the text and images in the thumbnail. This could be the operator of the third party website, or that site has licensed the content from yet another party. You haven't licensed it from anybody. So you can watch the content in accordance with the TOS, and your computer can evaluate the metadata to do it, but you cannot display it on your own site. Details will differ between jurisdictions, of course. You might also be held responsible for illegal content in the thumb you generate. Follow-up: There seems to be some question of what 'thumbnail' and 'card' mean in this context. This answer assumes a somewhat scaled-down representation of the content of the entire page, not just a collection of actual metadata like content length and expiry.
To do so I used some images and Gifs which may be under copyright but since I don't earn money for myself and there is no company backing me I was hoping that there is some protection for private persons like me who just want to showcase the project. Sorry. If your website is public facing (i.e. not password protected and available only to family and close friends), you need to follow copyright law. There is no exception to copyright just because a project is run by an individual for non-commercial purposes. I am also insecure about the GDPR regulations since I give users the ability to create an account and try it out. Your profile says you're in the EU. Then you need to comply with the GDPR. Is there any way to protect me against greedy lawyers and companies? Could I write something like: "This website is a peace of art" and save myself with arguments like "artistic freedom" or "free speech"? Nope. A controversial website run by Peter Sunde had at one point a "free speech" disclaimer (similar to the one you propose) posted. However, Sunde did never use this defense in court: Finnish court slaps Peter Sunde with €350k fine. If he had shown up in court, I am pretty sure the court would have told him that such a disclaimer has no legal merit. The only protection that will make you completely safe is to adhere to the law.
I've found Google's filtering based on licence to not be very reliable, at least not reliable enough to trust from a practical legal perspective. Using a photo that you don't own the copyright to is a risk. You may be infringing copyright by doing so. The owner may eventually ask you to stop, or they may sue you for damages. Further, some copyright infringement is criminal 17 USC 506. In my opinion, it would be unwise to use a work commercially that you don't affirmatively know you have permission to use.
I would argue that no, there is no copyright for the restored work. Independent copyright is only possible for any original material added, as previously discussed on this site. In this case, the added work was a technical process rather than a creative process, and technical processes cannot be protected by copyright. Copyright licenses would therefore be ineffective. However, I believe one could still impose a license based on owning the copy as opposed to the copyright (contract might be a better term in this case). However, if a third party managed to obtain a copy through some other avenue, any such contract would not be binding on them and nothing could be enforced against them unlike with copyright laws. Another way a license might be imposed is through patent protections, as technical processes can be protected via patents. However, I'm not as familiar with patent law, and this doesn't appear to be the claim being made.
Legal unless you violate copyright. Screenshots will probably be fair use. The manuals/how-tos need to be your originals, not copies from anywhere.
Is that extortion? false advertising? or in any way illegal? Not at all. The owner of the site is simply exercising his right as outlined in the terms and conditions from when the user signed up. And giving users an option for continued use of the site (that is, for him not to exercise a right of which they were always aware) does not constitute extortion.
If users were to copy dictionary definitions, for instance Oxford or Cambridge) and make the word lists public, is it a copyright infringement? If the dictionary entries are protected by copyright then your user has infringed that copyright by posting the dictionary entries. Am I responsible for this activity? No. But you may be responsible for removing it if you get a request. Can dictionary owners charge me against copyright issue? If you follow the procedures outlines in the DMCA you can be protected from liability.