How can photons give rise to two different spectrum?

'Emission spectrum' is when the radiator of the energy has the atoms in excited or ionised states that when they return to ground states release the energy differential. each released photon appears as bright line that is called its spectrum.
The same photon when passing through might get absorbed on way in a cooler medium (gas, as that would be convenient to explain) by an atom exciting it (raising its energy state) and would appear as a dark line at the same (frequency or wavelength) position against a background in spectral continuum.