I'm working on an app for iPhone that uses fitness tracker data. For my stretch goals I'm offering additional device support. Can I use a photo from the device company's news resource website?
You need to check the terms and conditions under which said images were publicized. Content on the primary website are usually "all rights reserved", so reusing them is not allowed.
But product releases are usually accompanied by "press kits" which include images licensed under more lax conditions so media outlet can use them to report about the product. But you still need to read those conditions to find out if they also allow your use-case.
When in doubt, ask the copyright holder of the images.