OK, now we have the 2 imagemaps for the back and the palm of the hand. To actually apply them to the
mesh object, we have 2 options: using procedural textures or using layered textures. The latter is
probably slightly easier but, for education sake, I have presented both.
Procedural Texture Approach
To set up the procedural texture, go to Scene -> Textures, select New, give it a name and select a Procedural 3D texture. This will open up the procedure editor dialogue window which will eventually look like that on the right:
Now the basic premise here is to control which of the 2 images gets mapped to which bit of the hand. The way to control this is through texture parameters. In case you don't know, you can assign points in a mesh with a specific value of a texture parameter thereby controlling how the texture looks at that point. Quite simply, we're going to have 2 parameters called back and palm. back is going to be equal to 1 on the back of the hand and 0 on the palm and palm is going to be the opposite.
First, let's get the images into the texture. Select Insert -> Patterns -> Image and double-click on the module that appears. This will display a dialogue allowing various image parameters to be set. Just click on the blank square at the top to select an image. This takes you to another dialogue where you need to click Load. Select the image of the back of the hand and click on Done and then OK to get back to the main procedure editor window. The image module will now show a thumbnail version of the image. We want this image to be mapped fully to areas of the mesh where back is equal to 1 and not mapped at all where back is equal to 0. So, all we need to do is multiple the image by back. Select Insert -> Color Functions -> Scale to add a Scale module. This has a colour input (pink) and a number input (black) and a single colour output. Plug the colour output from the image module into the colour input of the scale module, and the output from the parameter module back into the number input of the scale module. Now wherever the value of back is 1, the image remains unchanged and where it equals 0, the image will be black (colour equivalent of 0).
Repeat this whole thing now with the palm parameter module and the palm imagemap. Now we need to add the outputs of the 2 scale modules together and feed the sum into the Diffuse as shown on the right. So, for a point on the palm, palm equals 1 and back equals 0 giving an unchanged palm imagemap and a black back imagemap; the sum of these is the palm map and vice versa.
I have done one other thing in the texture on the right and that is to add bump mapping for added realism. I created greyscale versions of the palm and back imagemaps and smoothed them. I have then created 2 new image modules with these images and, using the same principle as above, mapped the bumps to the correct side of the hand (there is also a bit of scaling to get the bumps the right 'height').