In general photons are not candidate for dark matter.
From the other hand stars constantly change matter into radiations (photons among them). And we can not measure radiation that does not hit us (although we can try to calculate it because radiation from star goes with same intensity in each...
I'm starting my intergalactic travels project. Hmmm. It's even worst - I do not like Physics without concept of the aether. :D
And I'm here because in years to come hope to learn and discuss a bit.
Thanks!