Can sharing an image on social media without attribution or permission be considered as being fair use? For example, let's say you're posting the image of an eagle by someone, but you don't credit him and you don't get permission from him, but you identify what kind of eagle it is. Could this be considered fair use since like an encyclopedia you're effectively teaching what an eagle looks like, and what are the requirements to make that educational claim valid? Does it make a difference if the images are under creative commons?
If the person reusing the image (lets call that person R for reuser) is not complying with the terms of the Creative commons license, which include a requirement to provide attribution of the source work, then R cannot rely on the license, and the granting of the license ad the presence of a license declaration is legally irrelevant.
R must have some other basis to reuse the image. This could be an exception to copyright, such as fair use or fair dealing. Or possibly the image is not protected by copyright, for example because its copyright has expired, or because it is a work of the US Federal Government being used in the US. In the absence of such a basis, R is infringing copyright.
In much of the world copyright now lasts for 70 years after the death of the author (or of all co-authors). In some different terms apply, ranging from life+50 to life+100. Sound recordings and photos get shorter terms in some countries.
In the US the term is life+70 for recent works, but for work created and published before 1978 more complex rules apply, depending on the date of publication, and whether laws on notice and renewal were complied with. See the well-known chart Copyright Term and the Public Domain for the various cases and when copyright expires in each case.
The question asks about fair use. This is a US-specific legal concept. It is designed to be flexible, an is highly fact-dependent. As a result it is rarely possible to say if a use will qualify as a fair use with certainty until a court passes on it. See Is this copyright infringement? Is it fair use? What if I don't make any money off it? for more on fair use.
Not providing attribution is itself often considered to weigh against fair use. The question does not give enough detail to make even a good guess as to whether such a use is likely to be held to be fair use. Identifying the kind of eagle has some educational value, which might favor fair use to some extent, but must be considered in light of the overall purpose of the use, which is not described. There is no indication as to whether the original work is creative or factual, or whether the reuse would be likely to harm the market for the original. Much use of images on social media does not stand up under a fair use analysis. Providing proper attribution might well help any fair use claim.