Some of them are rather generic, and look only imperceptibly different from those of other vendors (e.g. resize arrows) – IANAL, but for those, I think copyrigh

Some of them are rather generic, and look only imperceptibly different from those of other vendors (e.g. resize arrows) – IANAL, but for those, I think copyrightability (threshold of originality, purely functional vs creative elements, etc) is open to question. Whereas others (e.g. busy) are much more distinctive, and I think the odds of them being protected by copyright (and trademarks too) is much higher.