In each situation where you are interested in using a specific work, you need to observe two questions which will determine whether any permission from someone is needed or not.
Firstly, an assessment whether the work is protected by copyright under the relevant law must be made. The presumption is that every piece of work found online, which has a creative nature is protected by copyright. However, certain signs may indicate that the work is provided to be used online in a free manner. Such indications can include marks of a free-license such as Creative Commons or an anti-copyright notice, which is the author’s explicit waiver of copyright ownership or of a specific right in order to encourage wide distribution of their work. Anti-copyright notices may be apparent in cases where the author has uploaded the work himself and can be similarly worded as the following: ‘The author of this work hereby waives all claim of copyright (economic and moral) in this work and immediately places it in the public domain; it may be used, distorted or destroyed in any manner whatsoever without further attribution or notice to the creator.’
Secondly, in order to determine whether any permission is needed an assessment whether the intended use will constitute copyright violation under the applicable law has to be made. The relevant legal basis in order to make this assessment would be the exceptions and limitations of copyright provided in your national copyright legislation. If your intended use of the work is identical with any of the formulated hypotheses of the exceptions and limitations, a permission and/or a compensation to the author might not be required. Chances are that the national provisions on exceptions and limitations would cover cases such as copying for private non-commercial purposes, distribution for educational purposes, etc.
If you are uncertain in the answer to any of those two questions, it is advisable to seek prior permission from the right holder before using their work. However, before commencing any direct contact with the right holder you must identify who the right holder in the current case is and which specific rights you would need permission for in order to exercise it. The right owner is often the author of the protected work whose name is indicated in a specific connection with the work. Permission for usage can also be received by a licensor who has acquired the right to use the author’s work by force of a licensing agreement with the latter. Next, you must determine what type of activities you intend to undertake since this would outline the scope of rights that you would seek permission from the right holder in order to exercise. Thus, when communicating with the right holder, it is advisable that you indicate all the specific actions you would commence in relation to the work since this would give him/her a clear perception about which specific economic rights he/she is supposed to authorize. The author will also have the right to require an appropriate fair remuneration in consideration of granting you the permission to exercise his exclusive economic rights.
Finally, if you manage to obtain the right holder’s consent to provide his/her work to you, it is advisable the permission is granted in a legally-sound form which will allow a long term retention of the statement and the ability to serve as evidence in any potential copyright litigation. Such a form might be in writing or a digitally-signed document in compliance with the applicable national provisions for this type of documents.