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The Graphics Pack tab shows the images, and has some good examples to get you started with formulas to display the images on your records.
The hardest thing to do is to choose the right images.
See also Using Image Formula Fields.
Setup
https://appexchange.salesforce.com/servlet/servlet.FileDownload?file=00P30000007NED0EAO
Which say only grant access to all users and go to the graphics pack tab.
Documentation
Notes
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