The relative velocity between two photons approaching each other is always equal to the speed of light (ccc). According to the theory of relativity, the speed of light in a vacuum is constant and is the maximum speed at which any information or particles can travel.
This means that regardless of the direction or relative motion of the photons, the speed at which they approach each other will always be ccc. This holds true for any observer, regardless of their own velocity or frame of reference.