In shallow water clear enough to disappear, a boat stops casting its shadow on the surface and casts it on the bottom instead. The metre or two of water in between records almost nothing, so the hull appears to hang above its own dark shape the way a bird hangs above a field. Nothing unusual is happening; the light simply passes through a medium that has stopped announcing itself.
The effect asks for conditions rather than luck. Sun near overhead, so less of it bounces off the surface and more of it goes down; pale sand to send it back up; and enough calm that the skin of the water is not busy scattering everything. Look longer and the anchor chain has drawn an arc across the seabed, a slow record of which way the wind blew during the night.
As a wallpaper this kind of frame is unusually well behaved. The weight sits low, in the shadow and the chain, while the upper half stays an open field of blue where icons and windows can go without covering anything that matters. It reads as a picture with room left in it, which is a rarer quality on a screen than beauty.
