To force a download of your file or folder, append ?dl=1 to the end of your Dropbox Link. Note that a folder will be downloaded as a zip file.

For example:

https://www.dropboxusercontent.com/s/xxxxxxxx/123.jpg?dl=1

To view the file (you cannot do so with folders) with the web browser directly without the Dropbox interface in your link, you can replace the www. portion of the url with dl.

For example:

https://www.dropboxusercontent.com/s/xxxxxxxx/123.jpg

will become

https://dl.dropboxusercontent.com/s/xxxxxxxx/123.jpg