I don't know that this will teach anything, but it's cool, and it gets at some stuff I've been thinking and writing about.
Go get a physical photograph. A page from a magazine will do, or a print, or a page of a book, whatever. You needn't tear it out, just get it in front of you so you can touch it.
First examine it as a physical object. It's a sheet of paper, probably. Some thickness. It smells, feels, sounds, a certain way. It has some sort of pigments or metallic deposits on its surface.
Now consider the pattern of tone and color on the surface, created by those pigments or deposits. What are the colors? Are they complementary, or what? What's the range of tone? What patterns are present in shapes and lines and masses of tone and color, on the surface of this piece of paper?
Descend further. Step through the frame now, in a sort of Matrix-like transition: What's it a picture of? Note the visual details. Is the man wearing a tie? Is that a mountain in the distance? Inventory the contents of the frame and place them in space relative to one another. Consider those relationships a little, and how that translates into visual relationships on the page.
Further. What is she thinking, is it hot or cold there, how heavy is that thing he is holding? What do you imagine about the scene?
A picture is always many things, and a photograph has the additional feature of having once been something real (usually).