The 3D image in a 3D hologram fan is typically an optical illusion, rather than a true hologram. A true hologram is a 3D image that is recorded on a 2D surface, such as a holographic film, and can be viewed without the need for any special equipment.
3D hologram fans, on the other hand, use a variety of techniques to create the illusion of a 3D image floating in midair. One common technique is called Pepper's Ghost, which involves reflecting a 2D image onto a transparent surface, such as a sheet of acrylic glass. As the viewer moves around, the reflected image appears to change position, creating the illusion of depth.
Other 3D hologram fans may use different techniques to create the illusion of a 3D image. For example, some models may use LCD screens or other display technologies to rapidly display a series of 2D images, creating the illusion of movement and depth.
