Use imgur to upload your pictures. The more important thing: You need to enter the url of the picture, not the side where the picture is hosted. Your picture's URL is
Use a service like imgur or somesuch instead; neither Dropbox nor Google Photos allow for direct linking to photos as far as I know, which means that they won't work when you attempt to use/embed them on the forums. As long as your image/file hosting service provides a link that looks somewhat like https://whatever.com/whatever.jpg (or whichever format you use) you should be good to go.
thanks gents, hmmm.... maybe not! Anyway thanks, sorted out even though Im surprised coz before I had it linked from dropbox and it worked but stopped. Something then must have changed with dropbox.
Its not worth doing If it doesnt scare you at least a bit!