It's up to the individual and whatever contract or agreement governs your use of whatever they did.
Some OSS licenses specify that credits have to be in particular places. IANAL, but I've seen cases where (when no location was specified) it was deemed correct by courts that the credit was in the application package (for a Mac app), which is not usually a place where people not reverse-engineering your app look. So you can probably get away with a lot as far as courts are involved.
That said, it's generally considered polite to put credits in an equivalent place to where you put the credits for your team/your main copyright notice. Not on the home screen, but your about screen or your Readme file are usually considered appropriate (the latter is the only sensible place for e.g. command line tools).
But when in doubt, ask whoever you're crediting where they want to be credited. Only way to be safe.