I get a lot of emails from artists asking about unsolicited solicitations from international organizations that propose to publish their work in a book (or to put their work in an exhibition). By default, I am always suspicious about these kinds of proposals and I urge you to be. In most cases, I find that these proposals are by disreputable people or firms that exploit the artists' desire to be seen and to further sales and their name awareness.
There is nearly always a substantial fee, rather than a licensing agreement that I would expect. So I urge you always to be suspicious. Seek advice, if you have to, but due diligence will usually reveal the pointlessness of the exercise to objective eyes.