Custom Gizmo.DrawIcon Images

I'm making waypoints (empty gameobjects / transforms), and I want them to be selectable (and visible) in the editor so I'm using Gizmo.DrawIcon on the objects.

I would like to use custom images for the icons, but I can't find out how to do that.

Where are the Gizmo Icons located? How can I import/use my own? Are there restrictions on the file type/size?

Note: Running Windows. The Gizmo.DrawIcon function requires a string for the location of the icon, leading me to believe they're all hiding in a folder somewhere that I need to add mine too.

Any help would be wonderful!

It's worded a little strangely, but the docs specify that icon images can be placed in Assets/Gizmos. So, simply create a folder called 'Gizmos', and import the images there. (I can't remember what image formats are supported, but I'm pretty sure I've used PNGs with no problem.)