There could be a picture of an X that is itself an X. For example, there could be a minimalist picture of a square that is itself a square. The picture could even be titled in such a way that it is or is meant to be a picture of itself, so that this square is a picture of this square. But in general a picture of X is, obviously, not X. A picture of a unicorn is an oil painting, say, and an oil painting is not a unicorn. The famous portrait of the Duke of Wellington by Arthur Lawrence (1815-1816) is most certainly not the Duke of Wellington himself. It has outlived him for by a longtime, for example. We can of course say, looking at the portrait, 'Oh look, there's the Duke of Wellington. I can see why they called him the Iron Duke.' There is a difficult and interesting question here about depiction, and how to construe the first of these statements. It cannot mean, 'Oh look, there is a picture of the Duke of Wellington
This is an observation about a picture in a material sense, gold frame and all.
Nor can the statement mean,
'Oh look, there is the Duke of Wellington, in a picture.'
Of course the Duke of Wellington could be sitting in a hole in the canvas, so that he is literally in a picture, and it could even be the Lawrence portrait. Nor can the statement mean that the picture resembles the Duke of Wellington, since the Iron Duke really wasn't two-dimensional or made of paint and canvas. There are far too many respects in which the picture actively fails to resemble the Duke for there to be any sort of overall resemblance. There is the fact that the Duke had legs, and the portrait has none, and a million others of the same sort. In the same way, the visual experience I have when I see the portrait is not the same as the one I would have had had I seen the Duke himself. It would be only in very special circumstances that I might mistake the portrait for the Duke, an unlikely mistake anyway since I know that he died in 1852.