It seems like it is possibly to do this by uploading the icons to an issue. The important part is to then go to "Manage Attachments" in that issue (which I could not find in the new layout, so switched back to the old layout), and then copy the url directly from the link at the file name. Do not follow the link and let that URL resolve. Use the link as it is under "Manage Attachments".
However If some user do not have access to specific issue types then how icon image url will not be accessible.
Please suggest.