An illusion is a consequence of a shift in perspective, and something that is not in the predefined context of how the brain perceives things. Some things seem completely perfect at the first glance, but give it a moment, and you learn something new.
Here are some of the illusory photos that will make you take a second look.
These are two islands, and also a violin.
Perfect couples or complete strangers (chuckle)?
Standing on hands or feet?
Is he above the ground?
Look at this one closely without getting confused...