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Upon checking your form, I noticed that provided URL's in the widget are being transferred as HTML instead of images and this is why you're unable to see the pictures.
I went ahead and used the direct URL of the pictures and created a cloned version of your form here: http://form.jotformpro.com/form/43384114414953 please take a look at it and let us know if it works on your side. If it does, feel free to clone it to your account.
In order to get the direct URL of your pictures, you can right-click the picture and click on "Copy URL of image" (this applies to Chrome, but it should be similar with other browsers)
This is the picture I see when I follow the link you sent me…
I did a little more testing and noticed that imagetitan changes the direct URL of the uploaded pictures from time to time, I've updated the new URL's and the slider looks ok now.
However, since they automatically change the URL of the pictures eventually the URL's will be broken and will need to be updated again. Therefore, I suggest that you change your image hosting provider to a different one such as Google Drive, Photobucket or Dropbox which provide a direct URL for the uploaded files.