There are many pictures on the Internet, like the one below, and many videos that show you how they created this effect. One of them is also below.
This is actually a 2D image that was painted on the sidewalk and must be viewed from a very specific angle. Here’s a youtube video showing how they create similar 3D street art.
Below is a smaller scale 3D art project and how it was created on paper. It’s a rose that appears to rise above the paper to the amazement of anyone looking through a camera held at exactly the right angle and height!
Having come from a family of artists (my mother painted with oil and my brother Jeff painted, drew and sculpted before he became a psychiatrist), but with no real talent personally to draw like this, I’m really amazed by the sheer genius of these artists!