A proportion of what I do ends up on this blog in the public domain. I restrict some of my work to non-commercial use but much of it is freely usable. This has the limiting factor that when I create something, such as a circuit diagram, chart, manual or 3d model, I have to only include things that I have created myself.
There are times when it would be a waste of time recreating things that others have already done. This would be for common icons, signs or symbols. I've previously mentioned standard components for 3D models and some sources for those can be found on the following linked page:
https://blog.discoverthat.co.uk/2019/12/sources-of-components-for-3d-models.html
At the moment I'm working on a car circuit diagram and wanted the standard ISO symbols for the dashboard warning lamps. Too many of the top results from searches took me to sites with a pay wall where the alternative free version required each icon to have separate attribution, which just does not work on some documents that I want to share.
If I was creating documents commercially then the nominal fee needed would be well worth it, but I'm not, I give my stuff away for the benefit of others.
Here I will list those sites where I have found creative common and more importantly public domain images that can be downloaded for free:
https://commons.wikimedia.org/wiki/Main_Page
https://commons.wikimedia.org/wiki/Category:Dashboard_SVG_icons
https://commons.wikimedia.org/wiki/Category:92/58/EEC_style_emergency_exit_signs
I'll add more sites as I find them.
==