Creating a model of a human head is extremely difficult to do. However, most 3D artists will need to approach this task at least once in their career. As soon as you have a well laid out mesh model of a head, you then have to devise ways of coloring and texturing the surface to stop it looking like a piece of plastic. All of these tasks will take time and a great deal of effort. However, the rewards from successfully creating a realistic head will teach you both modeling and materials creation like no other process.
Blender offers a huge range of tools to UV map an image to a mesh model. UV mapping unwraps all the mesh faces onto a flat surface. Once we have a UV map, it becomes easier to paint or apply photographs to this flat map rather than using other projection methods to apply a texture to a model. Photographs are probably the easiest method of creating the color map for a UV mapped head. However, UV maps tend to be distorted compared with a camera...