I was looking over the help wanted ads for software engineers recently. One particularly caught my eye. It was a startup advertising the availability of jobs, but with a catch. The jobs were non-compensation. You were expected to work for free. Presumably for the same sort of "credit" factor as the book cover photo job offer.
Now I personally don't like the idea of software developers receiving nothing in order to just receive a resume credit. I feel it cheapens the value of the work that I do, and potentially drags down future compensation levels for everyone in this field.
However, I also recognize that not everyone else in the field necessarily sees things as I do.
For example, given the state of the economy I could understand a newly minted computer science graduate deciding that the resume experience garnered by working non-comp right now might be better than having to later explain not working at all. And after the economy improves that the resume entry itself might later translate into greater compensation over someone who had lesser overall experience.
Ultimately, offering a low- or non-compensation job will, like everything else, seek and find its own level of credibility in the marketplace. If the job has no value whatsoever, then no one will take it. But if it has at least some value to at least one person, then the "eBay effect" will apply. An item is worth whatever someone is willing to pay for it at that moment.
As I said, value can be pulled from a transaction in many different ways. My pure speculation is that someone somewhere will take the book cover photo job as offered, if they have not already.
And I cannot pass judgment on that person's motives in doing so, as I will not have walked a mile in that person's shoes.