After uploading your image to the “Assets.xcassets” folder, you will need to find the “Attribute Inspector” on the “Right Side Inspectors” tab. Focus or click on "View Image", which you should place as a holder on the storyboard. On the right tab under the attribute inspector (looks like a down arrow next to the ruler) you can select an image from the drop-down list. You can also change the content mode to Aspect Fit while you are there.
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