unless you can clearly show that he's directly taken the work of someone else and modified it
Well luckily we can show this directly for a good third of the book, so there is no problem there.
In fact some text statments are 1:1 the same as in tutorials provided.
Even some artistical mistakes are the same as in the online sources just to take the AA example, but there are a few more)
some charts are clearly taken from sources which weren't mentioned.
That already proves that it's more than merely a coincidence.
Copyright law and law in general also depends on the country - at least for details.
In this case however one doesn't even need to look closely, because it's obvious. A quick glance over the source tutorials and the book does the job.
chapter 2, 3 and 4 off the book are clearly plagiarised from online sources - if you take all sources in account 95% of what's written in those chapters was already there. (28 sites filled with content)
practically chapter 1 (introduction) and 5 (closing tutorials) (those are 25 sites filled with contentthe rest of the 67 sites are book cover/table of content etc.
Some stuff in chapter 1 and 5 would definitely count as "derivated work" or it would need a proove, if you are looking at it just from the law side, that it's plagiarized.
There are some notes in the overview below.
Just from the rough numbers more than half of the actual content of the book is plagiarized.
All the basic art knowledge which isn't related to software and is contained in the book is plagiarized.
since the books is about fundamentals and clearly advertises the fundamentals of the art the problem from the law-side is quite obvious.
For example for chapter 2/3/4:
I made a tut on game perspectives and brought examples from games plus some further links to a chart from facet with more examples and a tut by pix3m showing perspectives simplified.
In the book there are my words, words from pix3m and the same games/examples as I took for my tut and facet took for his chart.
THe actual work done was just cutting together the sources and maybe adding a line here and there - and this covers already 9 sites of the book.
Kiwis tuts are also rearranged, also mixed up with some stuff I talked about with him back then and this covers 13 more sites.
Then there is a part with Helms dithercharts which cover 2 sites more.
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original content in the book 12 sites for the book cover, the table of content, chapter header sites etc. (can't be counted as content sites)
3 sites introduction / what is pixel art
7 sites - chapter 1 - choosing software /setting up ps for pixel-art (imo there is even a tutorial for that around) your first pixel artwork (albeit obviously inspired by my 5 tips for the beginner artist - at least structural and pix3ms what the heck is pixel art) -
11 sites - chapter 5 (which includes 2 original tutorials by the autor - one of those reminds me strongly of a car topic we had in pixelation)
1 site index (which can't really be counted as "original" content)
3 sites photoshop shortcuts (which can't really be counted as "original" content)
End of the Review.