Downloadable logo for visitors ?

[inside1000]

Many webmasters allow visitors to download their logos to their desktop to use as a shortcut.
Many times when your on a website that you want to create a shortcut to for yourself, when you right click & add the shortcut to your desktop the companies logo will appear instead of the standard browser icon. The company has set it up that way.
This is what I need to do but need starting points.

Thank you for your input.