hmm... not an expert at this. But there are some links published in past threads. I think, like Tom said, don't try to make it too perfect. You are working at the pixel level, so can change anything you'd like. I'd work with as high a resolution scan as you can. Make a mask using "find edges", adjust levels, Gaussian blur. Much of the personality is captured in the eyes, so even with crinkles I would not change too much. Also, for grins, make portrait of self. Combine with cracks. Beautiful.