Thomas Eliot works multiple themes in the poem, however in general, his usage of imagery mainly represents ageing and decay. In the lines "When the evening is spread out against the sky / Like a patient etherized upon a table", the phrases like "sawdust restaurants" and "cheap hotels," the yellow fog, and the afternoon "Asleep...tired... or it malingers", represent decay. The character's concerns about his hair and teeth which is mentioned in the lines "Combing the white hair of the waves blown back / When the wind blows the water white and black," show the problems about aging.
The speaker often refers to images having to do with the city. He refers to many locations and features of architecture that are present in cities, such as "one-night cheap hotels," "chimneys," "doorways and sprinkled streets," et cetera. He also personifies many things, including fog, the evening, and time. Hope this helps.
