Portfolios are a good heuristic, but you can't be sure the person actually wrote the code/took the pics, which is why you need some other way to verify they're actually capable of producing that work, not just copying it. Hence technical interviews.

Even for a programmer with a portfolio, it's vital that you be able to probe them with questions about design decisions and expose someone who didn't actually write it.

Does photography have some sort of solution to this problem? Can you ask a photographer about how they took a picture to easily reveal whether they actually took it?

I'm guessing there's less of a need to verify skill with photographers since most of the work is on a gig or piece-work basis where it's easy to terminate the relationship or refuse payment in case of obvious frauds. OTOH, what stops an unskilled from stealing a portfolio (or using with their consent) to get work? What happens if they produce usable work, but which doesn't look anything like the quality suggested like their portfolio?