A visual illusion is a phenomenon where the perception of an image differs from reality. This occurs when the brain interprets visual information in a way that creates a misleading or distorted view. Common examples include the Müller-Lyer illusion, where lines of equal length appear different due to arrow-like ends, and the Rubin's vase, which can be seen as either a vase or two faces depending on focus. Visual illusions can reveal how the brain processes visual information and highlights the complexities of human perception. They are often used in psychology and art to explore the relationship between sight and interpretation, demonstrating that what we see is not always what is there.