If I use a piece of code taken from free access (without indicating the license on it) in part of my project, have I violated any legal frameworks? Or should I indicate in my project the author, whose piece of code I took? And does he have the right to demand from me the obligatory indication of his co-authorship (if, in the place where I took the code, his authorship was not clearly indicated)? Can he demand to remove not to use his workings out? How can you prove your authorship for a code freely posted on the Internet? If my code is very hike to the code of some developer, and he expresses his displeasure? How to be in this case? How to understand where to begin and end the scope of copyright, relative to the source code?
If the code is simply uploaded to the site without a license, then you cannot use it in any way except to just read: the copyright remains with the author of the code, and only he can determine what can be done with his code. Fully define. Thus, if the author wishes, he may request that you list him as a co-author; and may require that they not indicate; he can also prohibit the use of his code (for example, saying that the code is laid out only for training purposes). Everything is in the hands of the author.
There is the concept of "public domain" (public domain), which means that the author waives his rights to the code, and anyone can do whatever he wants with this code. But in this case, it should be explicitly written on the site. By the way, as far as I know, in Russia it is impossible to give up copyright, that is, you cannot transfer your creation to the public domain - it can become public property only 70 years after the death of the author.
In any case, if the license code is not specified, you should contact the author directly, and find out the conditions for using his code. If your project is serious and large, then these conditions should also be legally formalized so that there are no problems in the future.
About similar codes, and "where the frames begin and end." In some ways a philosophical question. Here, in my opinion, nothing can be said except the following cynical statement: in court, you can prove anything you want, if there are lawyers and money. Some try to read the law a hundred times in order to understand the great idea that was laid in it, and then logically consistently draw these very frameworks. Lawmakers are trying to mention in the law all possible cases that can only be (and the authors of the programs write huge texts of licenses, where everything is written for all occasions) - and all the same, they and others will look at something, and get a clue using which it will be possible to interpret the law / license ambiguously. Idealized ideas about copyright, protection of intellectual property and, in general, the law , in my opinion, have no rational basis and contradict themselves. (Anarchism, yes; and generally a controversial issue, so I will not continue).
Therefore: do not rely on your judgment about the things that the author kept silent - directly ask him about it; legalize everything you can; have money and lawyers.
Keywords: free access, no license. Prove that this is his code, he can not in any way. The code is not yet patented.
But from my point of view, whether or not to indicate it in the authors is a matter of your conscience.