A professional photo agency offers us (Wikimedia Belgium) a donation of images of art works. They now offer as a start these images with 595 x 842 pixels at 72 dpi. This size is almost double of that from a thumbnail size on Wikipedia. My own (not the most modern) smartphone makes images at 5.312 × 2.988 pixels at 72 dpi. Seeing the size of these images I think they are to low.