I use Dropbox on my mobile phone via their app without any issues, just check out some of my posts.
From what I can tell, the photos you want to paste a link for need to be in a "public" folder in Dropbox. Once in a public folder, you can then create various sub-folders like "Family, Food, Cars, Porn" or "Chilli" for example. Then once you open a folder like "Chilli" you'll see all the thumbnails on the left and a down arrow symbol on the right. Press/click on the down arrow and then select "share" from the options. Once you press "share" a list of ways to "share" will pop up. On the top of that list should be "copy link". Copy the link and then paste it wherever you want to share it.
Hope this helps,
Cheers..........