The reason why the pictures didn't get imported is that the dropbox links are not direct links to the pictures. You need to add to your CSV file links that load directly to the picture and nothing else. The dropbox links load all of their interface to show the pictures, that is why your importation didn't work.
When you correct the links in your CSV file, you can send it to our support email firstname.lastname@example.org and we would delete the previously imported reviews without pictures and proceed to upload the new file with the corrected links, so that you won't get duplicated reviews.
I am uploading reviews to my shopify store in a CSV format and I have a dropbox picture URL to add to my review. The review does add onto the website but the picture isn't there?