My favorite Keats poem is "Ode to a Grecian Urn".  There are plenty of images there--the lovers just before they kiss under a tree in Spring, the tree that never loses its leaves, the cow being led by the priest to its sacrifice, the town empty of all people and movement.  He uses the theme of beauty here, which is also a romantic element as the romantics celebrated the beauty of nature in their works.  Keats says that "Beauty is truth, truth beauty" and that is all you need to know."  With the quest for beauty and the urn as the subject, the reader can consider this quest positive--ideal beauty gives us an experience of the eternal or timeless; or negative--the very same contemplation reminds us of the transience of our own earthly existence.  This is also supported by the fact that Keats mentions the urn will be around with all these pictures still in the state they are in long after we are dead and gone.