Stock photo sites like Dreamstime and Fotolia both offer access to huge inventories of royalty-free images encompassing the full spectrum of human emotion, including happiness. These sites are searchable by subject and include many different types of images.
Dreamstime includes images of such stock symbols of happiness as the rising sun, rainbows and smiling people. There are many ways to interpret happiness and the enormous and varied gallery on the site supports most any interpretation.
Fotolia, like Dreamstime, is searchable by subject. Users can search for images which reflect or embody happiness or joy and thereby thin out the catalog to find only images which relate to those concepts.