I painted 10 pictures as illustrations for a poet who asked me to do it and promised we would share the proceeds. Furthermore, he promised to put my name together with his name on the book cover, as well as write a page in the front of the book about me, with a photo.
Now he has published the book at Lulu, with no other mention of me except a thanks for the artwork and dedication of the book to me.
I need advice as how to proceed in this matter, since I painted these pictures at his request and he used the digital photos for the book, I still have the originals.
Can you give me advice, I would appreciate it very much,

For business transactions, you should always have a legal, signed contract. That's my advice...

First step is to discuss it with the author and find out his intentions and understanding.

A legal, signed contract is fine if the project is big enough that you would pursue it through the courts. In practise, that can be very expensive, and many disputes can be settled with a discussion. Maybe there was just a misunderstanding.

If that doesn't work out, it's likely that Lulu will have some process by which a copyright infringement can be pulled from their site.

I personally don't believe in copyright as a form of imaginary property. My advice would be to figure out how to use creative commons. I don't want to start a debate, but either way, isn't this thread entirely off topic?