From the site:

With this site, we hope to provide you with a wide range of illustrations scanned from old books. Most of these pictures are wood engravings or woodcuts, fewer are etchings or copper engravings. According to the copyright laws of many countries, they belong to the public domain and as such they are free to use for personal or commercial purpose. For more details, please see our terms of use.
The resolution of the images displayed in the galleries varies from about 500 to 600 pixels in height; their width doesn't exceed 700 pixels. A high resolution set (approximately 2000 px in width or height, depending on the format) containing ten pictures, is available for download as a zip file.
Its content changes every now and then.
We hope you'll enjoy your stay.