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Perhaps you can share us the form and the links you are using?
You might need to use the correct embed link from Dropbox. You can check the guide I mentioned in this thread link: http://www.jotform.com/answers/619995.
Here's the direct link of the blog guide that I referred to: http://yougotme.hubpages.com/hub/Using-Dropbox-to-Embed-Photos-in-Websites-Blogs-and-Email.
You'll be using the direct image link so that they can be viewed in your Image Slider widget.
Let us know if that helps.