This photo restoration process consists of several steps:

• remove intensive stain with Mixer Chanel;
  
• remove minor flaws with Dust and Scratch filter;
  
• selectively applying Dust an Scratches filter to face
  
• paint the face with photoshop tooks/

We can remove dirtiest channel (usually it Blue chanel )

However as the resulting image will be grayscale and we loose the semitones.

So we will remove stain with Mixer Chanel.

Select Monochrome option to modify each channel separately.

Use -> Image ->Adjustment -> Chanel Mixer
         Red :              98%;
         Green:          +4%;
         Blue :               0;
         Contrast :       -4%.

     Add Contrast using Curves:

    Image ->Adjustment -> Curves (Ctrl + M )


                 Input:       24;

                 Output:       0;

                 Chanel :       RGB.
;

         Remove minor flaws with Dust and Scratch filter

            Use: Image -> Noise -> Dust and Scratches:

                           Radius:                24px:

                          Threshold:             0px