Take a random field over a sphere, decide that everything above a threshold is land, and you get coastlines, mountains, deserts and ice caps — none of them chosen, all of them inevitable. The only real input is the seed, and the only question is where the sea level sits.
Random per pixel gives a television static. Noise gives structure: the value at a point depends on its neighbours, and it depends on them at several scales at once. Add a low-frequency layer and a high-frequency layer, and you get something that looks like weather and geology at the same time.
Interference between octaves is what makes the mountains look like mountains and the coastlines look like coastlines, because the large-scale layer decides where the continents are and the small-scale layer decides what kind of place each one is.
The projection is orthographic: every pixel inside the disc is a ray from the centre of the planet out to the surface, and the surface point is rotated by the planet's longitude and latitude before the height is looked up. That means the far side is never drawn, exactly as on a photograph, and the limb is a true circle rather than an ellipse.
The lighting is a simple Lambertian term against the direction of the sun, so the terminator is the great circle where the surface faces away. It moves when the sun angle moves, and the day length follows from the declination.