Hi priyanka,
Follow the below steps:
1. Create a bar chart with the country and any measure.
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2. Now convert one of the marks to shapes. Drop country in shapes shelf
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3. Now create a folder with all country flags and add the folder in my tableau repository.
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4. Now go to Shapes shelf and click on more shapes andclick on the reload shapes.
5. You can see a list of flags in a folder.
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6. Select each flag for each country and click ok.
7. Now make a dual axis chart to get chart. Edit the sixe of shape and bar.
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Hope it helps!