JotForm is a free online form builder which helps you create online forms without writing a single line of code. No sign-up required.
We believe that if one user has a question, there could be more users who may have the same question. This is why many of our support forum threads are public and available to be searched and viewed. If you’d like help immediately, feel free to search for a similar question, or submit your question or concern.
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.