Flags, Stoplights and Images in Salesforce Formula Fields

Below are the examples Salesforce gives you for creating formula fields that will display images such as flags, and stoplights. At the bottom is a link for the full knowledge article.

Flags for Case Priority

This formula displays a green, yellow, or red flag image to indicate case priority.

IMAGE( 
CASE( Priority, 
"Low", "/img/samples/flag_green.gif",
"Medium", "/img/samples/flag_yellow.gif",
"High", "/img/samples/flag_red.gif", 
"/s.gif"), 
"Priority Flag")

Color Squares for Case Age

This formula displays a 30 x 30 pixel image of a red, yellow, or green, depending on the value of a Case Age custom text field.

IF( Case_Age__c > 20, 
IMAGE("/img/samples/color_red.gif", "red", 30, 30),
IF( Case_Age__c > 10,
IMAGE("/img/samples/color_yellow.gif", "yellow", 30, 30),
IMAGE("/img/samples/color_green.gif", "green", 30, 30),
))

Traffic Lights for Status

This formula displays a green, yellow, or red traffic light images to indicate status, using a custom picklist field called Project Status. Use this formula in list views and reports to create a “Status Summary” dashboard view.

IMAGE( 
CASE(Project_Status__c, 
"Green", "/img/samples/light_green.gif",
"Yellow", "/img/samples/light_yellow.gif",
"Red", "/img/samples/light_red.gif", 
"/s.gif"), 
"status color")

Stars for Ratings

This formula displays a set of one to five stars to indicate a rating or score.

IMAGE( 
CASE(Rating__c, 
"1", "/img/samples/stars_100.gif",
"2", "/img/samples/stars_200.gif",
"3", "/img/samples/stars_300.gif", 
"4", "/img/samples/stars_400.gif", 
"5", "/img/samples/stars_500.gif", 
"/img/samples/stars_000.gif"), 
"rating")

Consumer Reports™—Style Colored Circles for Ratings

This formula displays a colored circle to indicate a rating on a scale of one to five, where solid red is one, half red is two, black outline is three, half black is four, and solid black is five.

IMAGE( 
CASE(Rating__c, 
"1", "/img/samples/rating1.gif",
"2", "/img/samples/rating2.gif",
"3", "/img/samples/rating3.gif", 
"4", "/img/samples/rating4.gif", 
"5", "/img/samples/rating5.gif", 
"/s.gif"), 
"rating") 

Horizontal Bars to Indicate Scoring

This formula displays a horizontal color bar (green on a white background) of a length that is proportional to a numeric score. In this example, the maximum length of the bar is 200 pixels.

IMAGE("/img/samples/color_green.gif", "green", 15, Industry_Score__c * 2) & 
IMAGE("/s.gif", "white", 15, 
200 - (Industry_Score__c * 2))

https://help.salesforce.com/apex/HTViewHelpDoc?id=useful_advanced_formulas.htm&language=en#ImageFormulasTitle