pikle,the server is on my computer therefore the root relative path /images/img.ping should work as well as the root absolute path which is C:/site-root/mysite/img_folder/img.png but it could be anywhere the site is stored.And it does workThe question was: why it's not recognised by all browsers the same?
Some browsers will interpret the path the folder based on where you launch the link from and others won't. If it is hosted locally and you launch the page from an 'open' command in a browser, say FireFox, it will know that it can locally reference the file. Ultimately it may be a problem when you post your site live and you should always try and use relative paths whenever possible.