Demo of path:... image used as background-image (that icon)
Demo of path:... images as img src...
You can create such images in any SVG editor.
Path image "url" is a content of attribute "d" of SVG's <path> element. So this SVG element:
<path d="c 50,0 50,100 100,100 50,0 50,-100 100,-100" />
in CSS will look as:
div { background-image: url(path:c 50,0 50,100 100,100 50,0 50,-100 100,-100); }
Note: content of "d" prepended by "path:"