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Have you noticed those small colorful icons on the top of the browser page, when ever you visit a popular website? Yeah, those are called as favicons. These are small icons which can be used on every websites (to signify the website).
These images are available at google.com/images/icons/product/blogger-128.png
[Replace blogger with other google products & you can also tweak the size such as 16,32,48 etc]
If you see the Google products page you will see different smaller icons. These icons are relatively smaller in size about 5px. There are larger versions of the same available (up to 128px wide).
Here is all Google favicons in 128px:
