I consider this image to be 'work in progress'.
I photographed an oak tree trunk and worked on it in Photoshop (in greyscale) until it tiled relatively seamlessly.
I also made it 512 pixels square. This became a 2D texture for the tree model which I made using Onyx TreePro.
I used the pict as a bump map in Bryce 2. It's still not quite right. You can look at my previous Brycings here.