How to give the image path in the check box field option for a content type
Your image path needs a / before sites. Should be "/sites/default/files/test-image1.jpg"

If you don't have a / at the start, then it appends your url code to whatever page you're on. Example: node/1/sites/default/files/test-image1.jpg which is not what you want (broken image since it doesn't exist)