To a very great extent, our visual sense is not “objective” in that there is not a perfect one to one ratio between what we see and how we make sense of what we see. In fact, oftentimes our brain interprets what our eyes perceive based not solely on the visual stimuli we are looking at but on our cognitions and experiences.
(http://boomeryearbook.com/blog/2009/03/15/psychological-article-types-of-online-optical-illusions/)

Many online optical illusions capitalize on this common miscommunication between our eyes and our brains, and use it to create online optical illusions; especially of the Cognitive type. Thus, when looking at an online optical illusion, the human brain takes in the visual stimuli and then connects it to past cognitions and experiences, matching the stimuli to our cultural and experiential “Gestalt”, In other words, perceiving the online optical illusion in the context of what is familiar and previously stored in our brains as meaningfully recognizable.

One of the classical online optical illusions that illustrates this example is the “Message of Love from the Dolphins” by Swiss artist Sandro Del-Prete.

Hmmm. What do you see? Well, before jumping to judgmental conclusions about this online optical illusion, it’s important to know that psychological articles inform us that adults see something very different than does the typical child.

If you are an adult, you will probably see two individuals in an intimate position in this online optical illusion. That is all right. Most adults will see the same. It is because you have prior knowledge of what lovemaking is. However, I have to disappoint you. In fact, this image is not of two individuals in an intimate position.

Psychological articles advise us to perform this little experiment. Ask some small children with no knowledge of lovemaking to tell you what they see in this online optical illusion. Will they perceive the image as adults do? Psychological articles tell us the answer is no. In fact, they see nine dolphins in a bottle on this online optical illusion. You may be surprised but it is true. Take another good look to this online optical illusion to find the nine dolphins.

Have you found the nine dolphins in this online optical illusion? If not, let me suggest that you concentrate on the black spots within the picture that you perceived to be human figures.

When you look at this online optical illusion, you perceived the image in connection with your prior knowledge that is within your realm of familiar experiences.

However, for a kid, this online optical illusion is just a school of dolphins in a bottle because they do not have any knowledge about the intimate position.