Greetings from the British LibraryZenlan
Use Google Slides to create greetings cards and discover over a million images from the British Library's public domain photo stream.
Mine a rich source of decorative letters taken from illuminated manuscripts and old books, embed them individually or string them together to create word art.
Many of the images are line drawings, perfect for colouring in!
Not only cards, you can embed the images in a presentation, add them to the layout, create watermarks - there are all sorts of uses you can put them to. Full attribution and links are provided.
Google Slides has a range of tools to format and manipulate images, shapes and text elements giving you endless possibilities.
See the website and help pages for full details.