The correlation function for intensity interferometry of high energy photons emitted from an expanding quark-gluon plasma is examined. It is reiterated that the correlation function for identical bosons emitted from two point sources is given by 1+cos([Delta][ital k][center dot][Delta][ital x]) and will oscillate between 0 and 2, depending on the values of the difference in the 4-momenta of the two bosons ([Delta][ital k]) and the difference in their 4-positions ([Delta][ital x]). Integration over smooth, realistic sources, relevant for very high energy nucleus-nucleus collisions, gives a correlation function which essentially decreases monotonically from 2 to 1 as the momentum difference becomes large. The oscillatory behavior seen in a recent work for certain momentum configurations is caused by an approximation which amounts to including only those sources for which the space-time rapidities are identical to the photon rapidities.