Ugh, this didn't work out so well. I attempted a watercolor of a scene in Minnesota, on the back of a pre-stamped postcard from the Post Office.
The watercolor bit was done with watercolor pencils, which are like colored pencils. I lightly sketch out the images and shading, then I go over it with a paint brush and a little bowl of water. That's it. It's like cheating at watercolors. All the control you need is to not let one area bleed into another area by daubing or strokes, unless the effect is intentional. Here, you can clearly see my amateurish and inept pencil lines, betraying my lack of complete comprehension as to how this simple system is supposed to work.
Then I did the trees and land with black Sharpie. That was also a mistake, as the paper is already so thin that the Sharpie can't help but bleed through, but now the paper is also quite damp from being soaked in water. The other side is almost entirely unsuitable to be written on, yet I had the audacity to write a short message and a destination address, when really this card should've been mercifully shot behind a wood shed.
The mirror image was easy, though. I just decided where the horizon should be and replicated my watercolor strokes on either side of it. For the land, I drew a long, thin line, then punctuated it with short, graduating lines, ensuring equal length on either side of the horizon line. Easiest to do this by turning the card sideways and sketching quick, short lines down the length. After summing up the basic growth pattern of the few kinds of coniferous trees in the original photo, an impressionistic rendition of them was easily done with more scrawlings by the marker.
Let's just say this little project didn't turn out exactly as I'd hoped. It's heading to New York, which itself is funny because the recipient stated her hope to hear from people around the world: instead, she gets a wrinkled, stained little card from some aging kid in a flyover state.