Do you ever look at abstract art and think you can definitely make out an image that's 'hidden' within the brushstrokes? Or look at clouds and think you can see animals in them? Kids seem to do it so easily, and it seems to be something inbuilt in all humans from very young. However, the amount that you do this, and what you 'see' seems to be very dependent on the individual viewer.
What you see is a reflection of you
What I find particularly interesting, is how what you see within these subjective images, seems to be a reflection of what you're interested in. Rorschach (a famous psychologist from the Sixties) used ink blot pictures in this way, to understand how a person might be thinking subconsciously. This was called a Projective Test and is still used in psychoanalysis (along with tests where you complete a partially-started ambiguous sentence).
From Wikipedia: a projective test is a personality test designed to let a person respond to ambiguous stimuli, presumably revealing hidden emotions and internal conflicts projected by the person into the test.
Attributing meaning to art helps it resonate
Humans naturally try and see patterns in order to make sense of the world around them. Often, art might particularly connect with someone emotionally, if they have projected part of themselves onto the artwork. An abstract image that I make out as being horse-shaped, will resonate more with me than just some random shapes on a canvas.
Below I've shown three paintings from wonderful artists that I have 'seen' horse shapes in. I'd be fascinated to know if these were also what you saw, or if you saw something different. (I have drawn the shape I see with a pink line on the image, just in case what you see is different).
Top: Anthony Cudahy
Middle: Lola Donoghue
Bottom: Sally King Benedict