After seeing all this photos, I can say that there is not really big difference in terms of race between Bulgarians and other Slavs.
Many of this people could easily pass unnoticed as foreigner in Poland, Ukraine or Russia, though indeed many are more Southern European in looks and would probably be told apart from locals here due to Mediterannean facial features and pigmentation.

I believe more and more that Slavs are indeed one race (in which Balts, Hungarians and Romanians can be included), some sort of Eastern European race. Of course that in group shots of Russian or Polish people, one would see higher frequency of blondes, this is no surprise, but I take back what I say before that South Slavs have racially nothing in common with North Slavs (some time ago on SF, but still). There is just more blondes in North, but I believe now there is lots in common between all of us racially and in photos like this, it shows. If this was taken in Poland, I would say that many of people could easily be Poles and others that look different could be Romanian.