I'm taking the liberty here, to post a personal experience that just happened to me in real life designs, that can help others the same way it helped me about it.
For
new users of dropbox, as myself, when you download the program, it doesn`t come any longer with the public folder, so you can`t afterwards get public links in order to post your drawing appropiately anywhere. But our friend
Kilomuse, who also is a new user and had the same problem, discovered that once you get the link to your drawing, when you want to use the Img tool, by replacing the "www." in the URL given for your link, by a simple "dl.", the program will work perfect and you`ll get your drawing to be seen, as how you expect it to be.