It depends. Is it public domain? Then yes. Otherwise, if you find something, it is probably owned by someone else. So either you need permission to use it, or you need to modify it substantially and make it your own. What we advise is to find something you like and make it better. Improve upon it.
We also recommend checking for a creative commons license:
If the art/logo has a creative commons license then that may be a good sign! The following creative commons license are ones you should be looking for are the following:
All CC licenses require that others who use your work in any way must give you credit the way you request, but not in a way that suggests you endorse them or their use. If they want to use your work without giving you credit or for endorsement purposes, they must get your permission first.
You let others copy, distribute, display, perform, and modify your work, as long as they distribute any modified work on the same terms. If they want to distribute modified works under other terms, they must get your permission first.
You let others copy, distribute, display, perform, and (unless you have chosen NoDerivatives) modify and use your work for any purpose other than commercially unless they get your permission first.
You let others copy, distribute, display and perform only original copies of your work. If they want to modify your work, they must get your permission first.