Anyone submitting work to Reactive Imaging for reproduction in any manner must be the current copyright holder or have rights from the copyright holder to reproduce such work.
In the United States, limited copyright protection of creative work is granted upon creation and transformation to a tangible form. This applies as much to music or text as it does to photography or illustration. From this point, the copyright holder is entitled to enforce exclusive rights or grant limited reproduction rights to others. A circled "C" serves notice to viewers that the work is copyrighted. A cautious user that did not create the work, seeks written permission to reproduce something even without the encircled "C".
According to the Berne Convention Implementation Act of 1988, a copyright need not be officially registered for the copyright owner to begin exercising his or her exclusive rights. Nevertheless, registration of works (where the laws of that jurisdiction provide) has benefits; it serves as prima facie evidence of a valid copyright and enables the copyright holder to seek statutory damages and attorney's fees (whereas in the USA, registering after an infringement only enables one to receive actual damages and lost profits). Original copyright holder may be the employer of the actual author rather than the author himself if the work is a "work for hire".