10,000 pictures from the Finnish National Gallery, newly online under CC0 Creative Commons.
Not all have preview thumbnails, but those that didn’t have one still gave me the picture as a high-res download. DPI on my test samples varied from 96 to 300. Most pictures, with a bit of adjustment, would be usable in a magazine. A few of my test samples looked visually as if they were quite highly compressed in JPEG, despite their file-size. Either that or the camera’s focus is not always as crisp on the picture surface as it might be. But possibly that’s done on the principle that users would rather sharpen in Photoshop than try to unsharpen.
http://www.europeana.eu obviously can’t be relied on the pick up all public domain items at the Gallery. Because a Google Images search for site:kokoelmat.fng.fi keyword found several “cat” images marked ‘Public Domain CC0’ that Europeana couldn’t find. Possibly that’s a result of Google’s A.I. automatically identifying what’s in a picture, and not relying only on metadata.