Finding high quality copyright free icons for computer diagrams in IEEE or ACM submission
The quoted part means that you don’t have to follow the license if you are allowed to use the icon anyway (without the license).

This could be the case if the icon is in the public domain, if its use would be allowed by something like fair use, the right to quote, or similar.

In other words: the license can’t restrict you from doing something which you are allowed to do according to copyright (and other relevant) laws. Copyright licenses (like CC BY) give additional permissions (under certain conditions), not additional restrictions.

If you don’t know for sure that the icon is in the public domain, or that your use would be legally allowed, better assume that you have to follow the license.



Most licenses require attribution. All of Creative Commons’s licenses do (as they all have the "BY" component).

If you really don’t want to attribute your icons (the attribution doesn’t have to appear next to the diagram, if that’s what you are concerned about), you have three options:


Use icons that are published under a license that doesn’t require attribution. It doesn’t have to be a known copyright license, it could also be stated in the terms of a service of the icon site.
Use icons that are in the public domain. The author would have to state this somehow (e.g., by saying "public domain", or by using the public domain dedication CC0 1.0, or one of the other public domain equivalent licenses), or you would have to know that the intellectual property rights have expired.
Use icons that don’t meet the threshold of originality. Of course it’s not easily possible to know if that’s the case. Better be safe than sorry and assume that all except the most simple icons are eligible for copyright protection.