Fair enough. But the point remains the image is still rendered in the mind. We can speak and exchange information and alter those images, and all this imagery seems to occur on a metaphysical level. I find it perplexing because "in the mind" does not necessarily equal "in the brain" or "just behind the eyes", as it seems. Experiments have shown that we are readily fooled by the body transfer illusion.
What body transfer experiment has ever shown that a person doesn't feel like they are located atop of a pedestal of a body? Even if you are able to fool someone with a VR machine that they have a different body, they would still feel like they are located in the head of that fake body. Rubber hands only work if you put the hand next to their real one and stimulate it the exact same way, or else it doesn't work.
Here's an experiment you can try. Touch your thumb and index finger one one hand together. Now close your eyes. Now move you hand about, up and down, side-to-side, and around. Pay special attention to the LOCATION of the tactile sensation of your fingers touching. Notice how the location, (and we all know location is always RELATIVE) of the sensation moves around and is ALWAYS located relative to the head. So it's not just vision that gives us a sense that we are located in our heads, but our other senses place us there as well. Why would it be useful to have a consistent location that everything else is located relative to? What would it be like if we didn't have this consistent location that everything else is located relative to?
If we accept that the triangle is in the head, where might it reside and in what form? One possibility would be that the triangle exists as an abstract "seed" form in the brain, akin to 1s and 0s in a PC (albeit using a different "machine language", one that will ideally be learnt) so that the triangle may be a small holographic projection from those bits. But where is that projection? It's not going to come up on a brain scan but perhaps will appear on a dream recording machine https://www.youtube.com/watch?v=MElU0UW0V3Q
I don't know, of course. Just bouncing ideas.
The problem here is that you haven't realized that your visual field is just a model, and an imperfect one at that. What you see isn't how it really is. This means that when you look at someone's brain, you are experiencing an imperfect model of their mental activity, or processes. You can never get out of this model and therefore never experience someone's mental processes as they experience them. You only experience a model. When you look at their brain activity on a computer screen you are looking at a model, not the real brain, and the model provides information about some state of the brain. This is no different from how we model the world in our minds. We don't experience the world as it is. We experience a model of it and to complain about the inaccessibility of other models is to not understand the nature of your own model.
I explained this a while back in this thread. You can never leave your own mill and you can only see other mills from the outside and only from within your own mill. So other models are out there, it's just you can only model their process of modeling the world and that model is the brain and it's activity.