You normally buy something from a retailer (someone whose business involves selling stuff).
If you buy something off someone, there's usually an implication that the person you bought it from isn't normally a "trader" AND/OR that you had to "persuade" them to part with the thing in exchange for your money (you "haggled").
This [potential] difference won't always apply, but it's worth pointing out that you'd probably never encounter I bought my Christmas turkey off a supermarket this year (that would always be ...from a supermarket).
In OP's specific context, we're not told what "these" are (the things bought off/from the wedding photographer). But the speaker would be unlikely to use off if what he'd bought was the pictures of his own wedding, taken by arrangement.
Using off would be much more likely if he'd bought something "unexpected" for the context, such as some unusual camera lens filters that the photographer just happened to show him (and was persuaded to let go for a price).