What does "image courtesy" mean?

[Jack Chou from China]

When I read a "ALL RIGHTS RESERVED" of a book, I found the following sentence: Image courtesy of the Singapore Tourism Board and Image China

I can not understand "image courtesy" well, does it mean that the author of the book has been allowed to use the images by the Singapore Tourism Board and Image China, or just let tell others where the images are from (that means the author has not get permission from the Singapore Tourism Board and Image China for some reason, for example, can not contact them).

Thanks a lot!

 

[Just]

Courtesy of ..... means being allowed and at the same time informs the reader of its source.