The Dutch national museum Rijksmuseum in Amsterdam has digitized 125,000 works from its collection. They're available as high-resolution downloads free for personal use. Another 40,000 images will be added every year until the entire collection of one million pieces is available.
You can create a free Rijks Studio account and categorize all your favorite images in folders, sort of like Pinterest. (Browse other users' collections here.) You could download your favorites and decoupage them onto your calculator or print them on tattoo paper and stick them all over yourself. Another option: recolor them and make stationery like these examples by Flow Studio. Have fun!
(Thanks for the tip, Jet!)