In Book 19, Penelope does not recognize Odysseus for who he is because he is disguised as a beggar. He expresses that he knows Odysseus and Penelope tests the validity of the alleged Odysseus sighting the "beggar" had by asking about Odysseus' appearance. She is satisfied with his answers and offers him a place to stay. She also offers him the chance to be bathed by the servants but he refuses. He knows they will recognize his body.
After some time, he accepts a foot bath. He figures that will not be too revealing. Unfortunately, it is. Eurycleia begins cleaning his feet and recognizes a scar that she knew he had. He commands her to keep the secret safe and she does. Thus, Odysseus' only recognizer is Eurycleia.