copyright law and the fairuse exemptions

Suppose i find some pictures in the garbage.
Are these pictures by their nature rejected- part of the public domain?
How do you find an author who does not want to be found, named or associated with a work. There are several thousand examples imagine the photography students who print several prints and throw away the ones they do not want. What about the photoshop that dumps thousands of rejected prints and negatives in the garbage.
Who are the authors of these thousands of negatives and prints that are rejected and discarded.
Suppose i were to take one of these obscure pieces of photography and mix them with other pieces that belonged to me and show them as a new work in a collection as a single piece (a collage) to my photography class. Would i be exempt from infringment of someone else's work if this new collage contained only 1 entire print of someone's work who could not be identified and mixed with my other prints?
I reside in the state of tx.

I am a law school graduate. What I offer is mere information, not to be construed as forming an attorney client relationship.

WHAT ARE WORKS "IN THE PUBLIC DOMAIN"?
The term "works in the public domain" refers to material that is not protected by copyright. Such works are free for anyone to use, in any way they wish, without permission from anyone.

The public domain includes material where the copyright expired, such as anything published more than 75 years ago, or where the copyright was not properly renewed, or material that was published without the required copyright notice prior to 1989.

One important exception relates to works of foreign authors whose copyright notice failed to meet U.S. standards then in effect. Although the work was considered to be "in the public domain" here, a recent treaty restored the copyrights of the foreign authors.

Material printed by the Federal government and certain other material that never enjoyed any copyright protection is also in the public domain. In addition, there are a host of matters that are not protected by copyright. They include ideas, concepts, processes, methods of operation, principles and pure discoveries. Also scientific and historical and biographical facts -- regardless of the effort and expense involved in discovering them -- cannot be protected by copyright and thus are in the "public domain". However, a book describing the expedition undertaken to discover the facts clearly can be subject to copyright protection.


It may be an abandoned copyright. But, if someone sees your work based on these pictures and he/she decides they want to enforce their copyright, they can still sue for the rights to your derivative work -- then it will be up to a court to decide what will happen.