Robinrohan,
You pretty much got the gist of what Quetzal said, but your analogy is flawed.... Yes, I would suggest that the image, such as that of the beautiful woman you are using in your example, is physical. But it is a different physical than what you seem to be proposing.
Take your analogy to the TV... In a TV an exact scaled replica in 2D is emitted from the screen based off of an input hundreds of miles away.... Yes, in that case there are certain set things you can measure physically (such as a scaled height). However in the brain, the visual inputs of different wavelengths(e.g.colors) excite different neurons in the eye. The signals are sent via the optic nerve and other pathways until it hits the occipital lobe (at the back of the brain) Here the information is divided up even farther.
For instance, you are looking at a red cube in bright light. Well, the photoreceptors in your eye, specifically the cones that respond to red wavelengths are activated and send their info to the brain. If you were looking at another color, a different set of cones would be activated and in low light conditions an entirely different set of receptors, rods, would be activated. The information sent from the optic nerve from the receptors is topographically (spatially in relation to the neuron input) maintained on its way to the visual cortex (I am trying to drop the really specific stuff here to give you an overwiew). Approaching the visual cortex, visual information is processed to 'recognize' edges and at the occipital lobe its broken down into stimuli from right and left eyes, color and non color, and orientation (what direction the stimulus was in).
So you see, even when you look at a beautiful women (physically), there is no mini beautiful women hiding in your brain somewhere... just a collection of electrical impulses that your brain interprets from past experience. So when you are imagining a beautiful women, your brain is firing a lot of the same signals, and some from the hippocampus (the center for memory) in order to produce that image. But the imagined is never as concrete as the original
.
Also, to help cement the idea that it is physical, like your TV analogy, certain physical aspects of a visual image, whether real or imagined can be measured through EMG (recording electrical signals from firing nerves), from experiments with PET scans, and the results from lesions in the brain. Place an electrode into a region of the brain and you can record signals, which correspond to sensory/motor input/output. You can also stimulate parts of the brain as well by applying an electrical signal, which will in turn cause a patient to feel what is not really happenning... maybe that their arm is moving etc....
Hope this helps a little,
Obsidian