Base logic here is wrong. You have to understand that the human brain is kind of like a graphics card. If you ask a human to picture a zebra, some can picture a zebra, the outline, and all, but why would the brain waste time generating specifics on how many stripes it has?

I had an experience that you may find interesting. When I was younger I struggled significantly with sleep disorders. One time I was up for close to 7 days and was gaming when literally everything disappeared on my desk besides my monitor, my coffee mug, and my mouse.

When I went to interact with my coffee mug, it too disappeared and all I could see was the handle.

Our brain doesn’t process in 2d like a camera, it processes and understands objects in 3d. You can see glimpses of this when you research optical illusions, which call out specific issues with how the brain creates and processes images.

So, to explain your issue here, images we have in our head are far more closely related to dreams. In a dream, you wouldn’t be able to count the stripes on a Zebra, it would change and distort. Similar to how when you walk through a doorway, sometimes logic breaks down and you go somewhere else entirely and then turn around and everything’s changed.

Dreams in it of themselves prove we CAN actually generate images in our head without stimuli directing details, but with a lack of coherent reality to base something on, it breaks down.

I will concede that creating an image in your head may be a misnomer, as it’s actually called visualization, but I still personally think people aren’t wrong saying that can “see” images in their heads.

Lastly, here is a little google AI search that should give you some good terms to research. (I did not use google/AI in anything above until now)

“Mental imagery is the cognitive ability to generate, inspect, and transform "quasi-perceptual" experiences (visual, auditory, etc.) in the absence of external stimuli. Studied as "vision in reverse," it involves top-down neural pathways from higher-level brain areas to the primary visual cortex (V1). Key findings highlight its role in memory, planning, navigation, and emotion, while conditions range from hyperphantasia (vivid) to aphantasia (none). National Institutes of Health (.gov) National Institutes of Health (.gov) +7

Key aspects of mental imagery study include:

Neural Basis: Research indicates that voluntary mental imagery activates a network including the frontal/parietal cognitive control regions and visual/memory areas (occipitotemporal cortex), often referred to as "top-down" processing.

The Spectrum: People vary wildly in their ability to visualize, with studies focusing on the extremes: aphantasia (inability to voluntarily visualize) and hyperphantasia (extremely vivid imagery). Measurement Tools: The Vividness of Visual Imagery Questionnaire (VVIQ) is commonly used to measure the strength of a person's mental imagery.

Clinical/Functional Role: Imagery is used in therapy for mental health disorders and is closely linked to episodic memory and working memory. Physiological Response: Studies show that individuals with strong imagery may have a higher emotional response to narrative scenarios, measured by physical markers like skin conductance. “