Start with an image of the relief you want to make. I have made good ones from scanned images, digital photos, and digital photos of images in books etc. It is good to start with a high resolution image if possible. It is best if it is lit squarely from the front to diminish shadows, but you can make a good relief even if the lighting is far from optimum but it is more work. If you make your own initial image with a digital camera use a flash and face the subject low and square on. When you have a suitable image open it in Photoshop or a similar image editor and trim any background from the object and duplicate it on a separate layer. Desaturate this layer and by using dodge, & burn tools lighten the areas of the image you think should be raised and darken those that you think should be lowered. Save this image and load it into the Bryce terrain editor to shape a terrain. Make the terrain quite thin but adjust the length and breadth to the to be relatively proportionate to the initial image. Go back to Photoshop & turn on the initial image layer & save it. Go back to Bryce and load this image into the 2D pictures & apply it as a material to the terrain. It looks best with frontal lighting but can look ok in other lights especially if initial image is well lit & sharp. It can take a lot of tinkering, I also used selection tools in Photoshop and adjusted the brightness and contrast and applied blurs. It is a process of trial & error you look at it in Bryce & then go back to Photoshop to correct any bits you dont like. I recently made quite a good face from one of my own digital photos & made a relief of it that was interesting but it took a lot of work.