Plagiarism checking software exists. Universities use it all the time. Surely, with a relatively narrow corpus of work like poetry, this is a trivial problem to solve.
From what my university professor told me (and some student friends of mine, who had their works checked by such software on regular basis), plagiarism checking software is mostly a joke (or a scam, depending on how you look at it), and is bought so that the university can tell that they are "employing best available methods of plagiarism-protection" when applying for government money. At least, this is how it works in Poland.
I don't know how big their corpus of poems is though.
Method b) is what, AFAIK, such software usually does, and from what I heard it generates tons of false positives and is generally annoying.
A student friend of mine told me about how much trouble she and her year has with the anti-plagiarism system her university uses; basically citing things or using the same reference material (and thus having similar references section) is enough to mark your thesis as plagiarism. They have a ruthlessly enforced threshold of "plagiarism %" you need to stay below, and from what she says, it's incredibly difficult to do so even when writing completely original work.
Sounds like your friend's school is misusing the tool. Seeing that students are all using the same references is pretty interesting information, as long as you don't leap to conclusions. Likewise, seeing that someone is not citing references properly may not be evidence of plagiarism but nevertheless it's good for students to adhere to reference standards. When I used Turnitin I had to keep below a certain percentge of 'quoted' text. I found this slightly annoying but I could easily avoid it by replacing a quotation with my own summary + a citation. It's just a stylistic choice that is being enforced through the system.
Also, no % of plagiarism should be acceptable - beyond the residual/accidental amount you get from coincidental phrasings.
Someone handed out a paper that looked excellent, I read it before he read it aloud, and I didn't believe he wrote it. It was too good and seemed above something a high schooler would write. I changed my mind and believe he wrote it when he read it aloud because the way he read it, he owned it. He read it just like it was something he wrote himself. After he was done the teacher said "that was good, but you didn't write this, you downloaded this from the Internet." She didn't ask him, she didn't check, she just publicly accused him. He looked shocked and said "No I didn't!" where she just kept insisting he did without any proof whatsoever except that the paper was just good. She may have just blindly failed him on the assignment.
Off topic but other student in this assignment handed out another paper which was full of misspellings and grammatical errors. Absolutely chock full of them, to the point you could hardly read it. After she read it, the teacher said "there's a lot of misspellings" to which she protested "my computer doesn't have spellcheck." She really thought this was a legitimate excuse, in English class. Like not having spellcheck excuses you from 1) proofreading and 2) picking up and old fashioned paper dictionary.
IMHO there's too much emphasis placed on doing things the "right" way and not enough on actually getting things done. Even if I did simply trace the photo, I still would have had a learning experience, engaging pencil, hand, and paper and understanding a bit more about how they work (to me, the purpose of the assignment). Regardless of how a thing is made, if it actually gets made and gets into other people's heads and gives them an experience worth having, I think it has done its job.
I took up my dispute with the vice-principle along with my parents and redid the assignment on thick, opaque card-stock (that couldn't possibly be used to trace through) and reproduced another photo with just as much accuracy. I went on to attend art school and win illustration awards despite my horrible experiences with art in high school, but I worry that another student might have abandoned their pursuit of art and deprived the world of their creativity, given such negative feedback. I feel we all need to lighten up a bit.
http://rochfordstreetreview.com/2013/09/20/f-for-fake-poetry...
> According to media reports one of the judges, Anthony Lawrence, became suspicious and, with the help of another judge (M T C Cronin) started googling lines from Slattery’s poem. They discovered that about four-fifths of the lines appeared to be the work of other poets.