#publicdomain?

Dear, Rich: I’m trying to properly attribute public domain images in a course pack I’m writing and I’m confused about public domain tags. If a work has entered the public domain without being directly dedicated to the public domain by the owner, there are nearly 100 tags listed under US copyright to indicate exactly why it is in the public domain (i.e. the copyright expired). Some images I’ve come across ask you to use these tags, while others don’t; meanwhile in Canada, there are only four different tags. My question is, do I need to use these tags to explain why it’s in the public domain when I attribute these images? Also, if I’m writing a course pack in Canada, but planning to offer it to American students, do I follow the tag of where the image was created, where it is being re-published, or where it is being “consumed” by students? There is no legal requirement that you include public domain tags. So why do they exist? Read on!
Label this! Copyright law lacks a labeling system -- some system that clearly and accurately identifies the copyright status (or lack of copyright status) for any work.  For example, the absence of a © symbol does not establish a work as public domain any more than the presence of the © symbol proves that a work is protected.
The problem with public domain works. Unless a court has ruled that work is in the PD, the potential user must make a private determination or rely on the kindness of academics and legal professionals. For example, if a work was published before 1923 in the U.S., it's in the PD. But questions may linger. For example, if it was a painting, was it "published" for copyright purposes. Other categories of public domain works create additional questions. For example, copyright does not protect typefaces, so it is assumed -- trademark law aside -- that logos consisting solely of a typeface are public domain. But that general rule may not apply to all typeface logos, and as a result a dispute may arise as to PD status. These PD disputes are more likely when there's a lot of money at stake. For these reasons, a system of tagging was developed by so that users of works would understand their public domain provenance and make decisions accordingly. (Stephen Fishman's book and treatise can be very helpful when sorting out these issues.)
What about you? You definitely don't need to reproduce these tags. If a work is PD, attribution of any sort is not required. However, for your own purposes, you may want to keep track of the tags in case a dispute should ever arise as to one of the works.
PS. We can't speak to Canadian copyright law but we have a feeling, the same rules apply.