The Rorschach is what psychologists call a projective test. The basic idea of this is that when a person is shown an ambiguous, meaningless image (ie an inkblot) the mind will work hard at imposing meaning on the image. That meaning is generated by the mind.
By asking the person to tell you what they see in the inkblot, they are actually telling you about themselves, and how they project meaning on to the real world.
But the inventor of the test, Hermann Rorschach, never intended it to be a test of personality.