Copyright law is intended to protect the income stream of the artist; etc. If you
"give away" with no intent to
"sell for profit" the work of another you are OK and clear of copyright law.
Many of the existing U.S. laws were rewritten in the late 70's and 80's to address the emerging computer technology. One no longer is required to add the copyright symbol or in fact their name; the mere taking of; or creating an image is enough for copyright authorship. Where the law now gets sticky is proving you were first.
It also gets real sticky on what is called
"derivitave products" from looking at a piece of artwork and being inspired to create another. If the original author can prove that the new work was inspired by his; he is entitled to a piece of the income stream generated by new piece. Even if the new piece is different and original by another artist.
Companies also must defend their ownership or lose their rights to it by not prosecuting offenders. Both Disney and Harley-Davidson are prime examples of this.
For all the nitty gritty details just Goggle U.S. Patent Office.
