It's stealing when copyright is infringed and when the stealing part is not acknowledged. Otherwise, can we called it "inspired by"?
Consensus differs on whether both, or just one, is morally objectionable. Conflating them is problematic.
In my own case as a designer of desktop apps, my Swipe File was not just digital screen shots of parts of apps that I admired, but I physically printed them out as well so I could spread them on a desk, floor, and walls when brainstorming.
That word "Swipe" also inspired the name of a design store catering to creative professionals in my home town, Toronto: