Aye, it's easy to composite sky photos into Bryce, that's what people have been doing all along in lesser programs, like 3DS and Lightwave (although now they have their own skymakers) Simply go to the Create Palette, and create a 2d face (square), and put it behind the scene, far away. Then stretch it to fill the sky in the scene, and THEN go into the Material Lab and tweak the ambience/diffusion and transparency, if you want. The only problem is that in reflections, such as in water, you might see the square edges of your object. Hi-res photos work best, or if you make a panorama you can always map it on the inside of a sphere object. Takes some practice, though!