The custom icons have to be in the directory of your alias file or in a sub directory off from it (which is what I did for the core aliases), so if you want google icon. Just create a icons directory inside the myaliases.alias directory and copy the google icon from the core alias icons directory.

Even More Information Tip:
To find icons, look in the core alias icon directory first and copy it to your alias directory; if you don't find what you are looking for, you'll have to find an icon somewhere or make one yourself.
A good trick to finding icons for a web site is by going to the site url + favicon.ico (Ex.
http://www.example.com/favicon.ico or
http://this.website.com/favicon.ico). If it doesn't find it then you will have to dig deeper by visiting the site then viewing the source code and see if the favicon is specified in it and piece the url together.
