1. Say I was at a Gig where you "could" take pictures. Could I then print that on to a tee and flog them.

2. Say I was walking down the highstreet and I snap someone. Could I then print that on to a tee and flog them.
Yes on both, but it is very unlikely that you will ever be at a gig where you "could" take pictures for commercial purposes. It will be in their T&Cs somewhere